Posting here for a quick answer as there is more traffic.
My mum is 46, she is slim, 5ft 9/10 and a size 10, she thinks she can't wear skinny jeans because of her age.
I think she can. I've seen girls less than half her age squeeze into them and look horrible. IMO it's not your age as long as they're plain denim, let's not get fancy now but it's how you look in general and they suit some people better than others.
Back me up here :)