I knew a bit younger than that. By the time I was nine I knew that I liked guys and while I was 12 I realized that I could also be attracted to girls occasionally.
On another note, since you are so early in the process and have not developed a rapport with this therapist you should consider going to another therapist. I find her approach to be questionable and it sounds like she is deciding to focus on your sexual identity in the therapy process. I know that in pastoral counseling we are taught to let the client identify problems and needs early in the process, and then later in the process we quietly direct toward some areas from time to time. I also find her tone in asking you "why" you were hiding your girlsfriend to be troubling. Generally 'Why' framed questions are accusatory and put a client on the defensive and most therapy and counseling training that I have seen avoids this approach.
As a counselor, I am uncomfortable with her focusing your sexual identity and would not want her to start pathologizing a healthy aspect of your identity. As a queer activist  who does a lot of my pastoral counseling with queer people I am a bit bothered by therapists in general who focus right in on sexual and sexuality based issues.
If you walked in and said you were having trouble in this area then those questions might be in order, not the approach that I would take but we are all different. 
At this early stage she really should be focused on finding out how you feel and what you perceive as difficulties in your life. This is not how a first session should have gone IMO. Please consider finding another therapist.

I think I've always known I was a little different, but it wasn't until I was about thirteen that I finally put two-and-two together. Before that "epiphany", I always kind of figured that men [u]have[/u] to be with women, but they find men attractive. Then in junior high, I realized that everyone was getting into a relationship, and it was weird for me not to have a girlfriend. So, I pretended to have feelings for a girl, and it crashed and burned. It wasn't until later, when my life in junior high was almost over, that I finally asked myself why I didn't find women arousing or attractive. That's when I found out.

Maestro,
I honestly dont even know if I want to see a therapist at all, I think I function quite well in my dysfunctional way, but good old mental health decided that I need to see one...anyway, I have another session on friday, ill see how I feel after that, if I am still not moving away from my 'gayness' then Ill request someone else.

Take care of yourself through this. 

I hate to start out with the same old tune of "I've always known I was 'different'", but I think for many of us, that's the truth. I didn't realize there was a lable for it until I was around ten years old or so.

I suspect that the therapist already knew the answer to the question she asked, and was hoping for transparency between the two of you. I can understand how that might have made you feel awkward or uncomfortable, especially if you aren't certain of the therapist's "motives". If I were you, I would bring up how that question made you feel at your next session. Therapy is all about the "relationship" between you and the therapist. A good therapist will respect you for bringing it up and it will make your therapy more meaningful - I promise!

And between you and me:

I think that everyone should go to therapy at least once in his or her life. Therapy is about delving deeper into your life, living life more fully, and living a more genuine life with others. It can be a wonderful, life-changing process.

I love my therapist, well, she's not really my therapist anymore cuz she moved, but she is amazing. She never asked me questions like that at all, I told her early on though.
But yeah, when did I know. I was twelve.. kind of. Looking back I think I should have known since I was about four cuz I was always all about girls. Then when I was twelve I realized I was bisexual.. well, I thought at least. I was really into this one guy so I thought I couldn't actually be gay. I was fourteen when I realized I was gay.

Well, I never had a "crush" to swear my friends to secrecy to, so I made some up back then. I thought it was fun b/c I knew I didn't really care if they told anyone lol. I didn't know what to call it early on...but I think the strongest signs for me were in middle school when I basically became obsessed with a girl. - Not in the usual "love obsessed" way but in general. That was also the time when I "really didn't like/want" to be gay. I had figured out what it meant by then. I also discovered the internet around that time and viola! lol

Oh and IMO society focuses way too much on sex. And therapists are usually no exception. Ive seen some at various times...or counselors I guess, and they do seem to be very intrigued by homosexuality and want to try and link everything to it. And I'm speaking from people who only find out after a few sessions...so yeah your situation seems extra strange. I wouldn't go back lol.

Well the reason I dont see why my sexual preferance is important is that I have been diagnosed with GAD (generalised anxiety disorder) and mild OCD (obsessive compulsive disorder) and I dont see how 'gayness' is a part of relieving my anxiety when I have no problem with it.

Well little_d I think that you should give the therapy a good try it has been of great value to me. Let the therapist know how you feel about those questions and their relative importance here.
A relationship with a therapist takes a while to develop.
When I am doing pastoral counseling (and let's face most of the folks who come to me for it are here because they ain't straight and wqould like to work with a person who can discuss religious matters and not have a problem with sexuality or identity) I find that a lot of things that seem isilated really are niot because you have to take a holistic view of the person and consider them as a whole person.
From the stand point of your therapist she may want  to see if your sexuality is somethng that contributes to anxiety or if the way you have been treated contributes.
Make an honest effort to communicate with your therapist, voice your concerns about this issue and try to build a good relationship.

Ok, I have my therapist session today, Ill let you all know how it all goes!

 I started being sexual with girls wayyy early on and was usually the "top". I think my first experience with a girl was when I was 7. My first experience with a boy was when I was 14. Quite the difference. It's interesting. With girls, I'm more aggressive, and with boys I'm more submissive. But I always knew basically that I wasn't hetrosexual and it was something that was very accepted in my household and I knew about every sexual orientation in the rainbow as a child.

But it took me a long time to figure out my gender identity that for sure.

 well let's see, i think i was about 12? i was in seventh grade when i realized it. i got a crush on one of my volleyball team mates, and yeah, that was it for me. no turning back from there.

Although I had my suspicions earlier, I didn't acknowledge to myself that I was bi until 7th grade.  Toward the end of that school year I realized I was trans.

 Oh, the question my lovlie friends ask so often :)
Lets seee...... when I was a really little kid,  I never thought about some dude in shiny armor, like the other little girls. Instead, quite the contrary. I thought about other girls (Angelina Jolie as Laura Croft :D), and such, until my dear, sweet *sarcasm* grandmother decided to tell my sister and I about the true sin of homosexuality and how it's a choice made by true satanists, and all homosexual people would burn an eternity in the firey pit of Hell *eye roll*. She convinced us that gay/lesbian people would cold bloodedly murder you on the street because they're such crazed disturbed people. Soooo, I shunned the possibiblity away from my  thoughts until I was in 5th grade, a year after my best friend came back from her 2 year trip to Virginia/North Carolina, and I developed a major crush on her. for quite a while, she was my only friend, and the only one I could talk to about anything ever at all-_-' Sooo, finally, afer thinking it through for the majority of a year, I decided I may be bisexual, I mean, I couldn't be a lesbian, now could I? *hah* So she was the first person I told, at the very very end of fifth grade, that I liked other girls. Never once did I mention I had a major crush on her, but I wanted her to help  me build the confidence to tell my parents. Instead, after acting different around me all through sixth grade, she suddenly stopped talking to me. It was sixth grade, after my first and ONLY boyfriend, that I became a lesbian. I was completely disgusted, dude. He wasn't my first kiss though.. that was Heidi, a girl, who made me doubt my sexuality after kissing me. Hm. :) But, now I have grown terrified of heterosexual males. Perhaps it's because all of the perverts I know, that are always all over me. Sooo...... Anyways, After coming to seventh grade, the "best friend" I had, told me, in all seriousness, with a cold tone, "I hate gay people," and thus began starting rumours about me. Who would have known?-_-'
 Sooo... I guess I've always been a lesbian, but wasn't positive about it until the end of sixth grade...