I would think that if your g/f felt the need to tell you that she would accept you, and remain with you, perhaps any time that you are ready to tell her would be okay.  But that is just a supposition, and none of us really knows how any person will react when we come out to them.

I told no one until I was 47.  One of the people I told was my brother.  Chances are, I could have told him MANY years before, as his response to me was, "you never felt like a sister to me."  Turns out that while he had no name for it, or understanding of it when we were young, he was aware that I was different from "other girls."  We were always very close, and after coming out to him, he said it always seemed that I was more like a brother would be. 

-Michael

I agree with Mike's sentiment, that she may very well accept you now. She might not, and I truly know how scary and devastating contemplating that can be. Please don't take this badly, but 24? Goodness! I wish I had come as far as you at... 40! Or 50! Live your life, my friend. 

Hi guys!

Yep 24, to be honest I wish it was sooner because theres some excruciating sounding waits for nhs services regarding gender.

Thank you both for the advice and support I really do appreciate it.

I told a close friend the other day, she was very accepting and supports me and it felt great to tell someone. I knew that I could count on her to be there for me.

Thanks again guys  x

If your experience is at all like mine was (and many others!) things could start happening very fast.  I started out cross-dressing (without acknowledging being trans), and almost immediately knew that wasn't enough!

Circumstances can of course dictate a lot, and fear of not being accepted is obviously a strong thing, but I agree with the others' sentiments about your friend and the likelihood that she'll stay with you - she may well have been telling you she already knows :-)