They did have hair dyes back then, mostly Henna-red or black. But I'm sure they were probably pretty 'noticeable'. And I have a feeling that dying one's hair would have been considered 'fast'.
Considering that it wasn't unusual for 16 yr old girls to marry, Agnes & Ada may be younger than we think. Agnes could easily have had Oscar at 17 or 18 which would make her early 40s, assuming he's around 25. Ada could be even younger. I didn't start going gray until my late 40s.
It's the problem with having a 44 year old actor playing Oscar and a 30 year old playing Marian. Yes, they do look younger than their ages, but neither of them looks as if they're their character's probable age, say 25 for Oscar and 20 for Marian. It 'skews' the way the rest of the cast looks in relation to them. But I suppose that's what 'suspension of disbelief' is all about.
Interesting that Carrie Coon (Bertha) is 41. Brett Ritson (Oscar) at 44, is playing her 17-18 yr old daughter's 'age semi-appropriate' suitor.
@NurseButtercup IDK about George having Oscar investigated. He knows he has the $$ to keep Gladys living comfortably without handing any cash to Oscar and he's from an old established 'top drawer' family, which is all that Bertha cares about. And what Bertha wants, Bertha gets. Now, if George should hear any rumors about Oscar's sexual escapades that might be a different story. BUT, since George is not 'socially accepted' it's highly unlikely that any unsavory gossip would reach his ears from a 'top drawer' source. In fact, they'd probably consider it quite a laugh if George's daughter married Oscar.