This may be a cultural thing because different cultures view adulthood differently.
Biblical times people got married around the time of puberty. We see that as children today but to that culture you was now a man or woman.
Some cultures say 13, some say 16, ours says by average 18. While other cultures go lower than that like Islamic regions.
I don't think the Bible says what age. It definitely has grave warnings for harming children. So what is the age of adulthood in a Biblical definition? It seems many examples like Mary and Joseph were quite young.
Biblical times of prearranged marriages to prevent being unequally yoked also.
God designed marriage for reproduction, companionship, and a system of disciplining carnal desires.
The age of puberty was often the case in those times possibly due to life spans being shorter. Or maybe to give woman more time to try and have kids because it is a scientific fact that,
“Women are most fertile and have the best chance of getting pregnant in their 20s.
This is the time when you have the highest number of good quality eggs available and your pregnancy risks are lowest.
At age 25, your odds of conceiving after 3 months of trying are just under 20 percent.
Fertility gradually begins to decline at around age 32. After age 35, that decline speeds up.”
https://www.healthline.com/health/pregnancy/best-age-to-get-pregnant#30s
So by age 30 especially back then, your risk of dying increased and chances of having children greatly diminished.