I don't care if they're older or younger, but they can't be too much older or younger! There's no magic number for me, where I'd say, "I could never date a guy X years older or younger than me." What was important to me when I was dating was the guy was at a similar place in life as me. For example, when I was in college I wouldn't want to date a guy who had already graduated and who had been in the professional world for a few years, because we would be at such different stages in our life, I'd have a hard time relating to him!
That being said, I've actually only dated two guys. My ex was 2 months younger than me (and teased me for being "an old lady", lol), and my hubby is 10 months older. I wouldn't have been opposed to dating guys a few years older or younger, but that's just how things turned out!