[WARNING: This post turned out quite long, and may be rendered useless to someone more experienced, but I'm trying to give some insight to the OP.
May you read this, thank you for your precious time.]
I can relate to this in many ways.
First off, I'm 20 (turning 21 soon), my ex-boyfriend is 21, so no great age gap here. Everything ended once he came back from a 7-day trip: his life wasn't at the right stage for us to be together. Or so he said.
After him I dated an 18 year-old who was quite into me, until his "secret" long-lost crush made its reappearance, leaving me out of the question. When we stopped dating I told him we were old enough to know what we do or what we don't. (He tried to justify his actions by saying he didn't know what was going on)
I've had 2 other guys having crushes on me, both younger than me, but I couldn't fully relate with them. Way too much younger than me, I was a complete disaster when I was their age. Plus one of them drinks HEAVILY and smokes an effin' lot, therefore confirming my point.
I can't be certain as how mature they are, but they're quite young, no wonder if they're immature, I mean I've been there too.
Now, on the other side of the spectrum, a 3-years-older-than-me bi guy. We had some sort of flirtatious relationship, but nothing ever happened because he never acted on his "hints". I grew tired of giving unrequited chances and stopped flirting.
Nothing was ever commented on this matter, but friendship's almost nonexistent now.
Recently I Facebooked a 22 year-old, same school, same this and same that, but even though I've tried to reach out to him, he hasn't shown any interest in return. Not even a "hello, I'm not into you". lol
All these people may seem lousy or immature (at least in certain aspects), but never had a chance to truly find out. In spite of that, I'm certain not everyone is like that.
For instance, I've just spoken to a 23-year old who may have some interest in me (we still need to find out), but not inside the flirting scheme. We attend the same Literature courses, so he invited me to his literary magazine project, making our conversations less shallow than stereotypical flirting.
That's my experience on age gaps, but regarding your specific question:
I think you can't really count on age to determine someone's maturity, you need to chat with them and find out. Perhaps you're looking on the wrong spots, I mean, clubs and bars are meant for fun and hookups, not for intellectual cogitation sharing.
Age gaps are different depending on your age, but they're mostly defined by your likes. I mean, I don't fancy dating 30 year-olds because I feel our lives would be at totally different stages, but for me it's a 10 year gap, half the time for you
I haven't had much luck with my dates, may them be older or younger, but I definitely find someone a little bit older than me a lot more attractive than someone younger, at least for now. And I won't surrender, there's a lot of people out there!
End of the line: Look everywhere! If you find someone you're attracted to, get to know them a little bit before dating. Or go further: look for people interested in your same activities, be it sports, arts, food, joga, or anything else... possibilities are endless!
