The biggest problem isn't the age difference... its really the 'life' difference.
I hated people when they would say things like this a few years ago, but the older you get the more you realize its true.
No matter how 'mature acting' you are, or how more intelligent you are than the people around you.. at 19, you don't know shit. most people assume once they turn 18 they're magically adults.. this is a lie.
at 20 you still won't know shit, but you'll know a little more than you did last year, same for 21 only you'll be drunk for a good bit of it.
I'm 22 and I can tell the stupidity is starting to taper off, but It probably won't be totally gone for another year or two.
Depending on how fast you mature, most of it will be gone around 25. In my experience i've dated people that were around my age, never anyone younger and at the most I think it was a 5 year difference. The older relationship is going to be a lot of them telling you things you think you already know but in reality don't understand and you won't realize that for a few more years.
It's sort of a harsh and fucked up way of saying it, but it's true. Have fun, enjoy it while it lasts, there's always the possibility that it could work out and be something more, but chances are you won't be anywhere near real LTR possibilities for a few more years.