Exactly this. The majority of super-popular names now will all be "old person" names in future.
In turn, the "old person" names of the recently deceased generations, like 'Florence' and 'Edith' are starting to reappear and be given to children again, because with that old generation dead they are freed from the old-people stereotype and seem good again. It's cyclical.
Amongst all names, there are some which are conversely a lot harder to date. Names that are always being given, but never top the popularity lists. Names like Mark, Thomas, or Matthew. Harder to date people with names like these, because there's always plenty of them.
I don't think I've met a John that's been in my school's growing up or was ever younger than me. Most of the James I've met have been older than me or Asian (since Asian parents often gave their kids traditional Western names to assimilate).