This is quite popular amongst parents where I am. There's also a big local push to avoid kids having smartphones before they're 13. Hopefully by that point they're mature enough to have a better understanding of what they're being exposed to, and are better equiped to know when to turn to an adult if something is upsetting or worrying them online.
Notably this isn't about restricting access to the internet, as kids have many other ways to get online at home, school, a friend's house, or even the library. Instead it's about ensuring they aren't exposing themselves to things they aren't ready for without an adult to guide them.
ETA: A lot of kids are pretty keen on this too, especially if they have had a bad experience online. The idea that none of their peers has a smartphone or social media means there's less peer pressure too.