A friend of mine is going out with a guy who's over 40 years older than him. They've been together for nearly 10 years now and are both happy. The young one did all the chasing. He's just not attracted to people his own age.
Another friend of mine from years back met and fell for an older guy. She was in her late 20s and he was in his 60s. Both their families were against their relationship from the start, but they stood up to them. They've been married for about 15 years now and have an 11-year-old son.
The largest age gap I've had in a relationship was only 12 years. I can't say I would rule out seeing someone older again, or, for that matter, some one younger, now that I'm approaching 40.
At the end of the day, it depends on the people. If you're turned on by older or younger and it's not a controlling or manipulative relationship, I don't see anything wrong with it. However, I've seen some relationships where a guy in his 50s is dating someone in their 20s and totally dominating them. That's not healthy. However, if it's a balanced, happy relationship, who cares how old the person you fall in love with is?