[ericd]

"People under 21 years of age made up over a quarter of the U.S. population (27.1%)" (https://en.wikipedia.org/wiki/Demography_of_the_United_State...)

So the population over 21 is about 230M.

[mac01021]

Hmm... That's a higher fraction than I expected. It could be much lower 20 years from now.

[ericd]

Yeah, very well could be if the birth rate drops or life expectancy keeps rising.