I've often wondered the same thing. The only things I could figure out was they got more of a head start from mom and dad.
I paid for and/or earned my college education, bought my cars, etc. No handouts from Mom or Dad.
Or they were in debt up to their eyeballs and it wasn't going to last.
Probably a combination of the two.
I was behind my peers because I had to pay Uncle Sam for that $50K college education in the 1980's with 4 years on active duty in the U.S. Army
I was working as a co-op engineering student and actually took a pay cut when I went on active duty. So I know many of my peers were out earning me out of the gate.
Some had student loans. Others like my roommate not only had the same ROTC scholarship, but had a healthy trust fund he didn't need to touch for his undergraduate degree.
He's over in Iraq right now, just pinned on LTC, so keep him in your prayers those who do that sort of thing.