Here, play with this fun little interactive map and see for yourself.

https://jonathansoma.com/singles/

I'll just quote the person who built this:

Among 20- and 30-somethings, almost every single city in America has more single men than single women. Although no single woman in New York will believe it, I promise it's true. Once you get up into your 50's, though, the balance shifts to extra single women everywhere. The changeover from extra men to extra women starts in the late 30's, but doesn't overtake California and the Pacific Northwest until everyone's in their 50's.

So the shift begins in the late 30s, which is later than red pill / manosphere guys like to embellish, but it does hit. The little chart at the top of the page clearly illustrates how women's power in the dating market peaks early and only gets worse with the two lines converging somewhere around age 35-40.