OK, I'm 62. I had DES exposure like KathyLauren, with assorted 'tells' growing up. It was probably in my early 30s that I became consciously aware of my gender identity, when I was interviewing a woman in the early stages of transition for a job position. At one point I thought "She's so brave to be doing this. I wish I could be that brave." Wait... WHAT? Oh, there were plenty of hints before, but I just thought I was a horrible pervy person and buried them deep.
(The DES issue is almost a distraction. I am what I am. Knowing how I got here is nice, but it doesn't change what I have to do.)
With a lot of help, I've come to understand that I feel my best, that I feel fully human and alive, when I can bring my gender presentation and gender role into alignment with my identity. That is, when I dress appropriately, meeting the social norms for female appearance, hair, and whatnot, and actively behave in a more feminine manner, including taking on the social roles we have set for women (oh, horribly anti-feminist sounding, I know, but it satisfies that primitive in the back of my consciousness that experienced the 1950s).
Yes, this means that I do such goofy things as put on my Gloria Vanderbilt jeans, a light top, old wig, and proceed to clean the kitchen, vacuum the rugs, and do the laundry. (This all happens while the wife and daughter are out of the house. They like the clean, don't like seeing MoPa...

). If I could greet them at the door in that Donna Reed dress and pearls I probably would, just for fun. It wouldn't go over well...
The point is that yes, I'm pretty sure of my gender identity at this point. Lining up the other bits, presentation and role, make me comfortable. HRT got rid of the internal conflicts, "testosterone poisoning", and is helping with presentation. The role is realitively easy, as 'enlightened post-feminist male' is close enough to allow me to do 'traditional female' for non-social role aspects. (I still can't get away with 'doing lunch with the girls' other than with my daughter, and I have to present male for that, even with the quiet giggling...)