When you think about it though, Plenty of 28-30 year olds take on $100K in debt and forfeit as much or more in lost wages to get an MBA. Through that lens YC and an angel round seems like a great deal relative to the network and opportunity you get.
Very few 35-40 year olds are going to give up 75% of their income for any reason.
Nobody's criticizing YC here though; we're all just making the obvious point that YC trends young because people with established careers in tech make a lot more money in a year than many YC participants will see in several.