The capitalist part that wants money can build an accurate enough profile with just statistical correlations, but the fascist aspect isn’t doing it “for the children” or even just money, it’s doing it to completely dismantle all digital privacy, so they can know what everyone is saying and doing online at all times.
If you grow up one of the tiny % of kids that grow up without one, it will result in some developmental disadvantages I think. On the other hand, modern social media will impose another set of disadvantages, but fact is that social media and the internet in general are a large part of modern society, so not being able to interface with it until you’re 18 will leave you behind a learning curve.
I don’t think there is any way to actually functionally verify age without either an ID check, or a check that ultimately traces back to an ID check from some entity further up the chain. Any successful age check will either dox your identity to the checker, or it can be trivially bypassed.
Someone who didn’t touch a phone until 18 is going to be so susceptible to scams, catfishes, propaganda, digital manipulation, etc, that I definitely think it is a dangerous nuclear option. Controlled, monitored by good parents, layered introduction is definitely better in my opinion.