its quite common, my hairline has been reseeding slowly for the past 3 years, i've also noticed that my hair is getting a bit thinner on top as well, there is a history of baldness in the family so i know i'm one day destined to have a bald patch.
for someone who is 19 it doesn't bother me too much because i know that there are other people who have similar problems.
Matt Lucas the comedian has been completely bald since he was 8 years old, so there are other people who have had worse problems and there are so many of us with reseeding hairlines its really nothing to worry about.
if in doubt shave your head, or grow your hair a lot longer so its all covered up. styling your hair with putty can actually be good for it... or so i was told! and you can style it to cover areas that are thinning