Age gap isn't a problem. Sad thing about society is that men are sort of expected to provide for their women. With all the "equality" going on, it's still the culture even in most developed nations. Men swoon over hot girls, women swoon over rich men. You'll get a job earlier than her, so in the long run, it's a nice thing to have an age gap. You won't feel it when 32 and she's 29, and even less so when you're 54, and she's only 51.
But if you can't see any future, then you should cut the cord while it's not too late. It hurts a lot more to break up after 6 years than it does after 3 years. And it'll lead to some resentment if she holds you back later in life. Just my opinion. I'm not really one for short flings with multiple women, better to find a quality girl I'd stick with all my life.
The age gap is nasty right now, though, because the USA will label you a sex criminal and put your name on the Internet for all your neighbors to see if you touch her when you're 18 and she's 17.
I've been in a spot where I dated a girl I never intended to marry. I couldn't enjoy it with her, I couldn't love her, and the closer we got together, the more I worried about how she'd feel if I dumped her. Eventually I did dump her. Both of us saw it coming.. she was pissed, I felt guilty, and if I could do it over again, I would've never dated her when I found out we were incompatible.
Some jerks would also say that you should stick around with her, until you find someone one better. But it's a douche move, and it'll look like you're cheating on her. I'd say just leave now and save yourself some pain later. You'll always find someone compatible with you, even if you're a weird fellow like Armok.