Sometimes age stops you from entering certain art contests for grants etc
Otherwise not an issue. If I change my mind and want to re-try to get into medicine, I only have one year before my undergrad degree becomes redundant for this purpose.
I thought it would be a waste of time to go on Schoolies because I was 17 at the time. And while I hardly drink, I knew that my age would make me look like a party pooper. But I have always wanted to travel somewhere with my friends without adults.