Many malls are doing this now and that's unfortunate. Most teens are law-abiding and many have the disposable income that shop owners covet. This is why in any typical mall about half the stores are geared towards teens. Restricting their access to the mall hurts business.
Sadly, PC dictates that we must punish everyone for the actions of a few with such blanket policies.
We have a curfew like that at a local upscale mall. My two teenage daughters love to shop there because it has all the stores they like. there are times they want to go alone (and I can’t or don’t want to accompany them) and they can’t because of it. and yes, they go there to SHOP and spend the money they make at their JOBS- not roam around in packs looking for trouble like the others that caused this curfew! So in addition, those stores lose a lot of money that the suburban youth would spend if they would just stop being PC and crack down on only the trouble makers.