Of course ageism exists, but it's less obvious as "radio won't play older women".
It deals more with the fact that women, as they get older, are expected to be less sexual and are expected to act a 'proper way'. This affects women more whose image is more sexual and whose music is poppier.
Women like P!nk can keep doing well because their sound and image fits on both Top 40 and Hot AC. Gwen didn't exactly light Pop on fire, but Used To Love You went Top 10 on Hot AC, no? It feels like ageism's impact on radio is less about not playing older women, but trying to faze them out of Top 40 and move them onto formats like Hot AC. This puts women who wouldn't get played there now (Britney, Madonna) at some disadvantage as they get older and radio play becomes harder for them to achieve.
Not sure if it's the stations themselves having ageist policies in their playlists, or just following the will of their listeners, who are ageist since society is ageist. Each format has its own issues. Not to say Hot AC as a format is racist... but the Top 50 on the format is really... similar.

I think Drake's the only non-white lead artist?..
It feels silly though to make it that it's ageism stopping Greatest from being played when Sia is #1 right now.