I would personally rather date someone my age or older, simply because in most cases, the older you are, the more maturity you have (not true in all cases, though). However, if a guy younger than me had a level of maturity that I felt was at least similar to mine, and a deep love for Christ, I would consider dating him. Age isn't a deal-breaker for me. Besides, I know three couples who are madly in love and have the best marriages I've seen. One, the wife is 36 and her husband 32 (and they met when he was 20 and she was 24), another couple, the wife is 27 and her husband is 25, and the last couple the wife will be 31 in October and her husband just turned 29. So, I've seen many instances of where it has worked out quite well.
Regardless of which direction, it would be strange for me to date someone with a significant age difference (6+ years), because then it becomes less likely that you'll have a lot in common, or that you'll be in the same stage of life (if that makes sense). But, again, not in itself a deal-breaker. I think it depends more on the person rather than the age. I've met 26 year olds who are very mature, and others who remind me of the middle school boys in my youth group at church.