Census says 4,021,726 americans were born in 2002, so 7 months since february: (7/12*4,021,726=2,346,006) + immigration...
I'm not so sure this is how we should read those numbers. It could also mean that the majority of young people reaching 18 chose to stay with their parents a bit longer because of the pandemic.
Isn't that mostly canceled out by all the americans reaching 30?
Why would you lean towards assuming it differs by such an astounding amount over a relatively short time period?
Pretty much, there seems to be a natural gradient pre-existing, where the age-in group seems to have a much greater natural affinity to be living with their parents even prior to the pandemic. We can all probably generate reasonable hypotheses for that, but that's the root of the mathematical assumptions.
[0] Here's a re-link of what I'm referencing: https://www.pewresearch.org/fact-tank/2020/09/04/a-majority-...