Fred also has that answer: https://fred.stlouisfed.org/series/POPTHM

Growing up to an estimated 342 million.

It also has an estimate for the working population (ages 25-54, so called "prime workers"): https://fred.stlouisfed.org/series/LNU00000060

Mostly flat from 2010-2021, with a recent uptick to 131 million. The discrepancy is likely due to the boomers aging out of the category, and a smaller generation coming in.

The youngest Millennials were 18 in 2014 and 22 in 2018. At this point, it's the smaller Gen Z entering the workforce, not Millennials.

Let me put it another way: the [20, 25) and [25, 30) age cohorts are larger than any cohort aged 50+ that might have recently aged out. So that "prime age" workforce is still growing.

This could be true, but it isn't obviously true (to me). (I dispute a little bit the idea that there are many new workers in the [25, 30) demo.) There are 37M workers 55+, but only 20M in the 16-24 range: https://www.bls.gov/cps/cpsaat18b.htm (2024 numbers)

Nobody in either of those cohorts is in the BLS "prime age" group which is [25, 55). The incoming cohorts that are now 15 to 25 are larger than the outgoing cohorts that are 45 to 55.

Ah, that makes sense. Thank you.