Just how dumb can a Popular Brain Myth be?

The Popular Brain Myth says that adulthood begins at age 25.

Let's think about this.

Our society prevents it from happening (as we should), but it is quite possible for a 12 year old to have a baby who grows up to have a baby at 12 years old and so you get a 24 year old grandmother. It's a bit less likely to get a 24 year old grandfather, but also biologically feasible. The claim that these people, who can literally be grandparents, are in fact children, is laughable :-D