1. It's legal
Fully grown men may not become romantically involved with teenage girls, because such behavior is a sign of paedophilia; and paedophilia is illegal and wrong. To be safe, fully grown men should only date fully grown women.
2. Women are less vulnerable than girls
Girls are too vulnerable. They make easy targets for sexual assaults and kidnappings. To protect young girls from rape, fully grown men shouldn't even think about dating teen girls. Men should date women, not girls.
3. Women are mature enough to have a family
Women are generally more independent than girls. They know how to take care of themselves, so they will probably know how to take care of children if they are blessed with children. Teen girls are not fully developed. Very few teen girls want to raise a family, unless the society around them supports young mothers and early marriages.
4. Female fertility peaks in the twenties
Teen girls may be too young to be fertile and sustain life. Ideally, a woman is married in her early twenties, and she only sleeps with her husband. A young woman in her twenties will probably have no problems with fertility issues.
5. Women are smarter than girls
Educated women should be more desirable than uneducated girls. Why settle for a teen girl, get her pregnant, and pay child support for 18 years when men can marry an older woman and raise a family together?