When people of each countries are below 18 years old and most of these teenagers are no job then do you think they are not paying taxes in the government because only the employed people are capable of doing, then it isn't because every goods and services that these youngsters tend to use in their daily lives are bond with taxes in general, it's same goes by with Bitcoin even though there is no government regulation that is straight taxing cryptocurrency in every single transaction.
How can a teenager get an income if the exchanges require you to be older than 18 and you also have to get a bank account to be able to use said income. This also requires you to be of age. If a teenager lies about the age and gets both a bank account and an exchange account he's risking a lot because if this comes out the funds will get frozen and the accounts will probably get terminated, unless the parents step in saying they knew about it and were supervising. What you're talking about is really a niche nobody cares about, just like that guy who gets tries to sneak a bottle of whisky through the customs. No big deal.
If im that teenager then i would normally make use of my parents credentials to avoid such problem regarding on what you have said here.Taxation would be just fine for me but shouldnt really be too big and should depend on the earnings we do gain on bitcoin.We do all know bitcoin cant be taxed directly this is why they are focusing on the things which are related to it.