Across Western countries, about 8% of all married heterosexual couples can be classified as having a large age gap (ten years or more). These generally involve older men partnered with younger women. About 1% of age-gap couples involve an older woman partnered with a younger man.

Is it wrong for a 17 year old to date a 21 year old?

Shouse Law Group » California Blog » Criminal Defense » Can a 21 year old date a 17 year old in California? Yes, so long as the relationship is not sexual. If they have sexual intercourse, the 21-year-old can face criminal charges for statutory rape if they are not married.