Laws on 18yr old dating a 21yr old?

The man is to always pay for dinner,

They should not sleep together on at least the first three dates.

What kind of laws are you asking about, there really is no laws about to adults dating, a lot of traditions and social rules.

Laws on 18yr old dating a 21yr old?
There are no laws preventing any legal age dating or sexual activities. There are several states that do prosecute for adultery but no one has been charged or convicted for those crimes in years. The only law that would prevent you from dating at that age is if you are mentaly incapabile and a custodian have legal capacity and that would be a problem then.