I can directly relate to your question. I most likely started losing my hair when i was 17, because by the time I was 20, I was really noticing a difference. I had really long hair in highschool, and I distinctly remember being 17 and thinking, "Geee, there sure is a lot of hair in my drain. Must just be because mine is so long."
So when I was 18 and starting college I decided to grow up a bit (just a bit lol) and get a nice hair cut. Well, it looked great, but I really noticed some receding temples for my age. I really just thought nothing about it, and continued on as if everything were fine. I mean, I'm a good looking guy............accepting hairloss as a reason for thinning hair? Unnacceptable. Plus, literally nobody, in my family is bald. Nothing to worry about right?
As time went on, my hair continued to thin, the temples haven't moved TOO much, but my crown and top of scalp have been doing sort of a diffuse thinning. I still continued to ignore it, and the time spent in the bathroom styling my hair was soon moving past the typical 2 minutes it used to take. Seriously, I was spending as much as 20 minutes refining the look, covering "thin" spots, etc.
At the age of 23, I was in about the same position as I was at the age of 21 and a half. Thats when my hairloss seemed bad enough to me to habitually wear a hat. The point, is that hairloss will not get better on its own if you have male pattern baldness (MPB).
The absolute best advice I can give, is to get into your doctor, and talk to him/ her about it. It really is an ego killer, and its a really tough call to make, but trust me, do it. Talk about finasteride/ propecia, and if your doctor is not knowlegeable about it, try and get into a dermatologist, they will know about it. Have your doctor make sure what you actually have is MPB, and if so, I strongly encourage getting on some sort of finasteride (Propecia, Proscar, Generic Fin.). This has been a God-send for most sufferers of MPB, ESPECIALLY if you start early on in the balding process.
In hindsight, I wish I would have manned up and gone to the doctor back when I was 18. I knew the problem, I just didn't want to accept it. You can rationalize away for a while, but it will catch up to you. So go to your doctor, and if you actually have MPB, get started on 1mg a day finasteride.