Its actually about biological maturity. Your brain is literaly not complete before that.
I can back this up with scientific sources:
https://pmc.ncbi.nlm.nih.gov/articles/PMC3621648/
“the brain rewires itself from the onset of puberty up until 24 years old, especially in the prefrontal cortex.”
“It is well established that the brain undergoes a “rewiring” process that is not complete until approximately 25 years of age.This discovery has enhanced our basic understanding regarding adolescent brain maturation and it has provided support for behaviors experienced in late adolescence and early adulthood. Several investigators consider the age span 10–24 years as adolescence”
Speaking from personal experience, i actually felt this. Its similar to the memory of suddenly “waking up to a compleye theory of mind” at around 5yo which many people have. Like the parts of my brain that were otherwise occupied in the background becoming fully accessible to me.
There might be some truth to what you say if you look at evolution. Cause it does seem like the phase maturity keeps getting longer, but its not something an insividual family can fight within a few generations.