Well, I can't date guys younger than me cos then they'd still be
in school. 
You think, *This girl here is really young!!* Yep!
So any younger, it'll just feel weird.
My current bf is a whole lot older than me. Above 10 years diff.
And before you call him a paedophile/cradle-snatcher, or call me a
slut. We've been together for a long time, and we're so in love
with one another, so it's a good thing.
And I've dated a guy who's 18 yrs older. It was kinda nice, but the
feeling was more like him showing me a lot about the outside world
rather.
But to answer your question, Yes, I would date a guy younger than
me if I was older than what I am now. And the age gap would be
probably about 4-5 yrs.
Why? Cos younger guys are so eager to please, so eager to learn and
willing to do anything to please you. They don't have the $$, but
it's ok cos I pay to feel younger. ha ha