Though I tried for an 18 year old last spring, didn't really go anywhere because of the age difference... so I think I'm gonna stick to girls within 4 years of me.
As long as she's not too old so her reflexes haven't gone and she can't play video games well anymore. If they're too young then they're usually better then me at gaming so I have to be very careful when choosing.
When I was 19 I went after a 30 year old. Was one of the sexiest women I've ever known. Didn't really get anywhere after she found out how bad the age difference was.
I hope you don't reveal that formula to any of your dates that are <21.5 years old. For they'd soon realise that whilst they are ok for you, you are not ok for them.