Maturity to invest is one thing and age limit is another thing. While there is no age limit to investing in a decentralized asset, there needs to be financial maturity to be able to make proper decisions and this does not come naturally. A background of investing in stocks, commodities, property can give a person an edge over others while investing in crypto.
I would not encourage kids to start investing in bitcoin, but their parents can start doing that if they are hopeful of the future of bitcoin, something like another forum member @BitcoinGirl.Club has done.
This is a tricky situation though, I would rather conservative about exposing young minds to a wild west section of the economy. Definitely needs a lot of maturity considering the number of possible scams going on here.