I had to deal with the same problem, since I started college with 16.
Now when I am graduating, I still have a bad feeling about explaining people why I am two or three years younger than anyone else in my grade.
Honestly, You shouldn't mention it if you don't have to.
I try to avoid mentioning anything related to age in a conversation, so that most of the people don't even ask me about my age. If it happens though, I consider if the person I am talking is just a temporary acquaintance, whom I will probably never see again. In that case, I tell them that I am three years older than I really am (even if I hate lying).
If a friend or someone I spend more time with asks me, I tell them my real age, since I think that they would discover it later anyway. I always attempt to act modestly so that nobody feels threatened or ashamed because of me. In addition, if you are in a good college, many of your colleagues will be probably really smart too and will have sympathy towards you.
I understand your worries about being labeled as weird or conceited, especially if you are an aspie too... But believe me, most of the people don't think that much about it if you aren't arrogant and reminding them all the time. My age was never a topic of a discussion for more than five minutes.