Your response is bewildering.
The author doesn’t rely on this as her only point. That’s a).
But, even if she did, she didn’t claim women are the only people whose brains are under development even into their young twenties. Duh.
Rather than blather on about somehow going aha! you’re infantalizing women, you might, and I mean might, be able to say: well, that’s ageist.
But let me give you some example which might help you out:
You know why priests preyed on children?
you know why Spacey’s victims were, in many cases, young men?
you know why Nassar serially victimized children?
you know why Levine assaulted young boys?
you know why…? I guess we could go on.
Because men and women, before they reach a certain age, unless they have been taught to deal with specific situations have a hard time dealing with certain situations, even us adults do.