I'll go 10 years younger, and up to 15 years older. I'm more flexible on the older part. I'm 31, so I can't go much more than 10 years younger anyway.
When I started dating again, I was trying to go +/- 5 years. It wasn't until I opened up the range that I met my current girlfriend--who is 9 years younger. But we've been together for two years now, so we must be doing something right.