But then it gets worse! They'll continue to do things that you consider stupid, but you can't control them any more.

My theory (slightly humorous) is that kids don't smarten up until age 27.

It does decline, but I think the 27 years is meant to include College, finding a job, a mate, a home - i.e. "launched" and independent. 27 seems to be a somewhat arbitrary number as is my list of "launched" criteria, but in the US kids can no longer be on their parents health-care plans after age 26. That's a significant milestone for many.

Perhaps he had multiple children, extending the range