For me, it's the fact that everyone looks the same. I will admit, I'm a bit vain and worry that women my age will look better than me with tweaks, but then, when you look, they kind of don't. They just look shinier and stretched.
Makeup can be creative. But now, going to the pub, everyone looks the same: lips, fillers, thick lashes, eyebrows. Sorry, the women do. Men are allowed to look however they want. I think it actually hides people's actual good looks behind an idea of what beauty is. And yes I know we've always followed fashions, but not to the extent our faces no longer look human.
It's a bit like in Brave New World, where the protagonist is shocked at the woman on the reservation, who has wrinkles because no one really ages in her part of society. Ben Elton covers it too.
I must admit to being torn. I want to age properly, I've earned every line, but I also don't want to look shit, if everyone around me is tweaking away merrily. But then, their faces aren't theirs anymore either. And it doesn't actually make you look younger - just better. But not really better either.
I go round in circles.