Men Over Thirty. When it comes to dating, what's your age cut-off?

So I've got a friend at work; just turned thirty. He's perhaps not the smartest tool in the shed, and whilst he does look thirty, I think if we were guessing his age by his level of maturity, we'd place him fairly squarely in the 18-22 age range.

Anyway, 30 has had this ongoing thing with this girl at work. She's 19. He sees nothing wrong with it, and whilst that may be true from a legal standpoint....most of us think it a bit ... untoward at best.

This post isn't about him though. It's about you. What's your age cut-off, both high and low for dating?