Back in the USSR.

[Tellos Athenaios]

Over here, and I guess in the UK we expect 15 year olds to have a little more knowledge of "how the world works" so to speak. Of things like accepting upfront cash payments of smaller amounts after normal working hours instead of larger fees in exchange for proper paperwork. Plumbers and other self employed craftsmen might propose that. I don't know about 15 year olds in the USA, but you can bet that payment is not going to end up in the books, therefore it won't be taxed.