Hi,
I went through a very similar situation to you.
I also have very thick hair and naturally had a high hairline with a slight curve at the hairline.
This very gradually got worse until i was 22/23 and I started to realise I was actually losing some hair on the temples. I told parents/GP and they all had the same reaction as others on this thread as my hair looked like yours. So I decided to wait another year before going on any meds in case it really just was a mature hairline, hoping it would not get worse, but it did indeed get worse!
I've now been on fin, minox and nizoral (the "big three") for around 9 months to try and stop the hairloss but to be honest it doesn't seem to be working for me! Perhaps I need to give it a few months more....
Anyway my point is that whilst your hair does look fine now as others are saying, you know your hair patterns better than anyone else, so I would keep a close eye on it as it may well get worse as mine has. At the same time, this may not be the case for you. The risk you take with going on medication now is never knowing for sure if it would have got worse without any (assuming the meds work for you) in which case you could be taking them for your whole life when you never needed any!