@frasier and he’d be old enough to get married in Kentucky NOW if he was a girl 
This is the sort of thing I would want to buy at his age - I’m still a bit ‘money burning a hole’ type!
My boys are a bit younger, but so far when they get money, what seems to work is to say if they desperately want it, then they can buy it - but just consider you could buy X amount of instead, or wait until they have another fiver and buy . Ultimately, I don’t say no because it’s not my money, but I do try and steer them towards waiting. In general it seems to work.