to answer the main post... 20/21 is when it was noticeable... 22 now, and still working on acceptance. In Hindsight though, it may have started as early as 18
ive had a receding hairline since i was about 18. now im 20 and the hairlines gotten drastically worse to the point of just being this thin strip. (its gotten worse since my default). i might regret saying this later but..........i almost wish i had no hair on top instead of this thin strip because it looks rediculous with my already large forehead lol. being self conscious is a bitch....
i started losing my hair at 17, but i actually shaved it at 20. I got tired of being in denial about it and having my hair make my head look like one of the Aliens from the movie, since the thick horseshoe made the back of my head stick out.