I'm no maths genius, but this wouldn't stop 15 year olds. Just those under 15.

I think it's perfectly normal to restrict things from kids and young teens that may be damaging. The same is done for other types of media like tv, movies, music etc.

Social media is more insidious in that, instead of art trying to inspire emotions, it is weaponising our emotions and addiction against us. Many adults can't handle it, but they can make their own mind up kids, we should protect as they can't make an informed decision.