I think it depends a lot on how old someone is when they come out also. My last BF was 30, about to be 31 in a few days; when I met him, I was 19, and I just turned 20. Things went sour, and I still have no clue what went wrong, he just started getting really distant. He wasn't cheating, I know it for a fact, but he just told me he's not in love with me anymore one night. Then he said about a week later when he was visiting friends in Florida that they had gone to boy bar and he made out with a few guys and did I feel uncomfortable if he slept with someone. I'm sorry, but less than 2 weeks before this he said he was on a downswing with his bi-polar condition and didn't want sex from anyone, it wasn't just me. He claims he never did sleep with someone since I expressed I would be hurt if he did.
Me on the other hand, I just turned 20, came out 2 years ago to the month and it was my longest relationship, 5 months. He's the second guy that's been 10+ years older than me, the first was 28 when I was 18. I have found that in general, it's not an age factor, it's an "I don't want to settle down with someone because I just KNOW there is someone better out there." I gave my all in my last relationship, and after 2 months, he stopped giving his all. He tried to make me feel guilty about wanting to have sex when he didn't, even though he would wake me up and want to fuck when I had already said I didn't want to. Even then, using the excuse that I'm too hot for him to resist, so trying to make it my fault. After 3 months of this, I was broken, exhausted, cranky, vulnerable, and depressed. I had a breakdown after we broke up, and he even said I was just trying to get him to feel sorry for me.
I don't think there's too much correlation between age and maturity, at least in the gay world. I've actually found most older guys are more manipulative since they've been at it longer. They tend to be really nice to start out with until they know you've fallen for them, then it's on their terms when you hang out, their terms when you have sex, their terms where you go out on dates, then they make you feel guilty for being honest.
I'm not saying all older guys are emotionally abusive, but the ones that are, are considerably better at hiding it than most young 20 year olds. He started telling me he didn't want a husband, he didn't like being seen as a couple instead of an individual, all that crap that doesn't matter if you really do love someone.
I guess there really isn't an answer to your question, don't just seek out a certain age group in hopes they're more stable, you could pass up a lot of good people who would treat you the way you should be and who want the same things out of life as you, you might just have to work a little harder at the relationship. Have your boundaries of age if that's your thing, but still be open to some young guy and don't just write him off for the age.