Millennials were only the "poorest generation" in their early 20s then they catch up. I'm sure the same is true for younger kids.

A large reason for this is that their parents live longer so they inherit wealth later in life (especially true for super-wealthy that distort statistics like this).

Yes, the age expectancy has been mostly stable recently, but wealth now takes a long time to inherit and you should compare boomer's expectancy vs their parents' (boomers' parents lived 20 years less long vs parents of kids today living 10 years less'). In other words, millennials were inheriting wealth 10 years later than boomers did. Boomers' parents expectancy was about 50 years so their kids in their 20s were fairly likely to have inherited something already.

College loans are also a factor for kids in their 20s, but they're a much smaller one (about 1/10th from my rough estimate).