I've been dating a girl 15 years younger than me for about 3 or 4 years. Assuming you guys know each other pretty well, and have determined that you have similar interests, goals, and expectations, then it's not really different from any other relationship.

That previous sentence may be trickier than it at first appears, however. Indeed, isn't it pretty much the reason any relationship will fall apart?

From the perspective of the older person, my primary worry was that my gf's expectations and lifestyle would go through a lot of ups and downs. She is really mature for her age, but I kept waiting for her to go through some kind of wild "period". Her capacity for "partying" and being wild has turned out to be pretty similar to mine, however, so this fear has turned out to be unfounded, so far.

I think a lot of our expectations with regards to sex and age involve cultural generalizations that turn out to often not be true. For example, I'm approaching 40 and don't particularly feel an oppressive need to get married, though of course I'm open to the idea. I'm also very active and fit. My girlfriend has a hard time keeping up with me, actually. And she is supposed to be this confused young adult "searching" for themselves, screwing up and learning from her mistakes. She actually is pretty goal oriented and screws up remarkably little.

Hanging out with her younger friends can sometimes be trying, but it doesn't take long before we all just forget about the age gap all together, and everything seems completely normal. There are a few though... that seem hell bent on living up to the above mentioned stereotype. I only hang out with them occationally.

In short... it can definitely work, I think it just depends on the people.