I answered ten, because I can't really imagine myself dating someone in their mid-thirties or beyond. I was tempted for "I don't care how old they are." but in the end I do care at least a bit. Other things than age also. Like being pretty and smart like me.
Personally I feel there's a generational gap between me (born in 92) and people over ten years older. The oldest of our class ('80) seems significantly different from the second oldest ('83). But that's about as anecdotal as something can get.