17, 18, 20... all these ages are arbitrary. Meaningless.
A female is either of reproductive maturity (adolecence/adulthood) meaning its perfectly fine to have sex with her... or she is not yet a viable candidate (prepubescence) and cannot reproduce.
Thats it.
Anything extra is you letting papers cacs typed up 50 years ago supercede human physiology and the biological laws of the universe that have existed forever.
"I'm gonna let this sandwich sit here on the counter for a few years cause white ppl say it isn't ready to eat yet."