I am mesmerized by the age 40 bar. It barely moves; a few more people are retired or are in school. My armchair speculation is that turning 40 really makes people reexamine their decisions.
If I try to create a startup I'll be doing it on my own.
EDIT: I disagreed with you, with a following comment, and didn't downvote you.
I'm not sure he's a great example. He has inertia and a lot of money made from when he was much younger. Take an average person at that age, middle class income, family, etc, and see if they can accomplish life changing goals that they just started chasing.
I'm not going to agree with the poster above that claimed that "At 40+ you realize you've pretty much accomplished everything you're going to with your life." but I think as a generalization it's probably closer to truth than feels comfortable (I'm 37).