Many 18-20 year olds live at home and the sum mentioned will not have to cover any living expenses at at all so will be pocket money to spend. Older people earning more will pay tax, NI and then all their bills and living expenses before they get to spend the disposable which may well be less than £6.15.
More valuable than the money to the teenager will be the experience of working, dealing with the public, learning self discipline, realising that life is sometimes demanding, having to think of others instead of just oneself and, hopefully, the value of saving and of knowing the value of things by having to buy them rather than having them bought by others. It will bring maturity and banish ‘snowflakery’.
An added bonus will be that, if the young worker, then goes on to university, they will appreciate the value of their loan and that they should not waste their time but get the best degree they can. They will also understand the efforts it will take to pay the money back.
Great dividends are paid later on in life when essential lessons are taken on board earlier rather than learnt the hard way later.