I don't think it really matters. As long as you have a connection, age is just a number. I'll admit that extreme differences in age might be a little odd, but who am I to judge. I've tried to become more tolerant of things. I try to think of them as "different" rather than good or bad / right or wrong.
I personally don't think it matters. What matters more to me is their age mentally. A guy could be older than me, but still mentally be a fourteen year old kid. I'd be uninterested in that.
I agree, emotional and mental age play into the choice. I've meet older women that literally act half there age. Considering she acts her age, I would prefer younger.
Let's see, I've mostly only ever had partners that were older. Oldest I've gone is 15 years older, hahaha! Youngest I've gone is I think 3 years. My current girlfriend is about two years younger than me. I'm quite okay with this.