or maybe it's because that stupid expression exists, and even in 2025 some people are still shamed by judgemental individuals who believe clothes have some weird age limit.
Of course there's a category of customers who prefers a more frumpy"mature" look and retailers cater for them. But if these custoemr wear what they like, why can't other people prefer something else?
The difference between "teen" shops and "mum" shops is more linked with size than style frankly. Teens are, or used to be, a lot slimmer.
You don't look older when wearing "young people clothes" (whatever the heck that means). At worst you look your age, which you would look anyway, but that's not even the case.
I read on a thread like this that you could be "too old for jeans". How would this be even a thing?