You are assuming that the girl's age changes, but it really doesn't have to for the situation the parent describes to be true -- the skill of not being an idiot

You are assuming that the girl's age changes, but it really doesn't have to for the situation the parent describes to be true -- the skill of not being an idiot can (far) more than adequately compensate for a ~15 year age gap... But it might be different for those who didn't start out as idiots :)