It's utter bollocks and I'd be telling her to wind her neck in!
I'm 46, my hair is down to bottom of my shoulder blades, I also haven't dyed it for some time so the grey is obvious too. Although I've actually been seriously considering a gorgeous sea-green colour a hairdresser friend recently dyed another friend with similar colouring to me (natural redhead, ghost white skin and freckles 😂)
My mother also thinks over 35 shouldn't have hair past shoulder length. She niggled for a few years then I got pissed off when once she was doing it in front of strangers to me basically "shaming" me for having "age inappropriate hair" a couple of the people were visibly embarrassed for me! Words were had no more said since.
There's absolutely NO reason for this, everyone's hair is different. I don't suit it short and actually find short hair MORE work than long.
I remember posting on another thread about certain generations having certain hairstyles (my grannies both had "shampoo & sets" weekly which were then "protected" by headscarves, my mums generation - boomers - seem to have commandeered the Bob, now whenever I see bobs I think 'must be a boomer', my generation seem to be the only ones exhibiting variety! From short spiky, to shoulder length and longer. Dds all seem to have long wavy hair with ombré and similar colouring).
I worked in elderly nursing previously, my residents would have been my great-grandparents ages so born 1910's/1920's and several had long hair as they'd always had, which they liked either in a single plait or bun. Sometimes (special occasions) we'd do a chignon or Edwardian pompadour. And they were in their 80's/90's!
Butterfly - who's the blonde in the last pic, I think a few of them are over 50? 60? Even? Yep - Jane Seymour almost 70.