If I don't have kids and can stop giving a ****, I could definitely see going 10 years younger, dating someone in their 30s when I'm in my 40s.
Right now, five years younger is early 30s and I feel like you get a lot of guys who still aren't ready for family life and are just slowing down from their 20s. I've gone on a few dates with early 30 somethings and it makes me feel like I'm back in my 20s, which is fun for like a month or two and then...I'm tired.
