Voting for my wife - although I learned to stimulate 'the spot' when she was in her 30s - she was in her early 40s when she learned to have a g-spot orgasm.
I started incorporating penetration into my masturbation when I was about 17, having developed a vague awareness of a pleasurable zone inside me, but I didn't really find the exact spot and figure out how to stimulate it until quite recently (I'm 20 now).
I didn't really find mine enough to have a gspot orgasm until I was about 20.
Before hand, I did squirt now and then but thought it was all the wetness built up behind the toy lol
I'm older than most of you. I remember debating in college with girlfriends whether G-spots existed but we didn't try to find ours. It wasn't until my late 40s, after I bought some G-spot toys, that I found mine.