When I was in my 20s, I would have said the same thing. :) I agree that there are mature 18-year-olds and immature 40-year-olds. I think you're discounting the role of practice, though. Someone with 20 years of experience has spent almost 40,000 hours at work. It's very hard for a 25-year-old to compensate for that no matter how smart they are or how many experiences they've had.
Story time: My grandfather was a soft-spoken old cowboy, but you should have seen him charm and intimidate cattle buyers. At 70 years old, he could hold his own with the slick-talking young buyers because he had gone through that same negotiation 100 times and there was no trick they could pull that he hadn't seen.
Story time: My grandfather was a soft-spoken old cowboy, but you should have seen him charm and intimidate cattle buyers. At 70 years old, he could hold his own with the slick-talking young buyers because he had gone through that same negotiation 100 times and there was no trick they could pull that he hadn't seen.
Disclaimer: I'm 39.