That's more of a preference. The "your age divided by 2 plus 7" rule is more about social acceptability of the relationship. But hook-ups are just sex, and generally not subjected to scrutiny, and that doesn't have to be acceptable to anyone but you and your partner.

Most people generally like to keep their partners in their age range, but it's very flexible depending on the prospective partner. And there are quite a few young people out there that do genuinely like more mature sexual partners even if they'd never actually date them.