I'm about to turn 30, so I only go 5 years younger at most. Even then they have to really stand out. I'm happy with up to 10 years older though. In 10 years time I will be happily shacked up with a really hot guitarist I would totally go 10 years younger.
My list...skinny, long hair a big plus as are tats, preferably no kids, has a passion for something (job, hobby, summat that they love to do), veggie or vegan gets big bonus points. I think my only deal breaker on the list is that they must read, I couldn't date someone who doesn't read a lot.