Its a very simple intuitive calculation that is used widely throughout epidemiology.
It feels like, with Covid, people try to add on unnecessary calculations or ignore important factors to shoehorn the numbers to fit a narrative.
7.2 million cases aged 50-64 [1]
58 million people in the US aged 50-64 [2]
So based on those numbers, 12.5% people in that bracket were infected by early November. From that you can attempt to extrapolate an infection risk per annum of around 8%.
Of course, now we're extrapolating from a time with varying degrees of voluntary and involuntary NPIs such as mask wearing and social distancing to a time where those won't be practiced widely, some of the time range we're extrapolating from also had the virus localized to regional or social communities, while now the distribution is more and more homogeneous. On the other hand, it's possible that virus spread will measurably decrease now that more and more people have some resistance through vaccination or past infections. So it's not a very reliable extrapolation at all.
[1] https://www.statista.com/statistics/1254271/us-total-number-... whether or not that number is accurate is debatable, our estimates of the true number of infected vary widely
[2] https://www.wolframalpha.com/input/?i=age+distribution+usa
All age groups are equally INFECTIOUS once they have the disease, but are not equally able to BE INFECTED , otherwise people under 55 wouldn't have to wear masks. We wear the mask to protect others right? No matter what our age is.
So why would you reduce the population size to just an age slice?
The same assumption is made when calculating herd immunity. They use the entire populations infectiousness because chance to transmit doesn't change with age but chance to be infected does..
But you DO limit by age group on the infection side because that individuals chance of contracting it from the general population, is based on age/immune system .
But it doesn't make sense to do #infected in age bracket / whole population size. You might as well calculate #infected in age bracket / number of cattle in Texas.
Of course there are many reasons why one would want to look at the number of infected in certain age (or social or whatever) groups. Beyond that, I'd prefer not to get further into the weeds with you.
That's the chance of infection.
This same idea is used in mask policy and is used with herd immunity calculations and all over epidemiology to be honest.
I'm really sorry that you have to do mental gymnastics to shoehorn this subject into your narrative.
Have a good day!
Total number infected until early November 2021: ~37 million [1]
Total population of the US: ~329 million
Infection percentage so far in pandemic: 11.2%
"Chance of infection" (per annum): ~7%
See above why this is an absurd extrapolation that nobody with any brains would take seriously. In the long run, pretty much everybody will get Sars-Cov-2. It's an endemic disease.
[1] https://www.statista.com/statistics/1254271/us-total-number-... per your source, NYT and Our World in Data refer to 47 million cases