Can a 18 year old date a 13 year old?

NO! That is highly illegal

YES, you can.... >.> IT IS illegal if the 13 year old is still getting through his/her childhood. But, once they get out of childhood and they're STILL dating... then, it's COMPLETLY fine... I mean, my mother and and father are 8 years apart... if a 13 year old dated a 21 year old.. Once the 13 year old is 20, the 21 year old will be 28. There's NOTHING illegal about it if they're 8 years apart. I mean seriously, it's not like they're 20 years apart! Jeez...