This would have been at LGW, where I suspect the agents are a bit more clued up about this area given that they deal with far more young travellers proportionately. At LHR if he looked mature enough he would probably been able to use the lounges but I guess could have asked for the voucher instead. The other option at T5 is he would have been given CCR access so that his alcohol consumption could (in theory) be monitored. But yes, in a way a long flight in World Traveller on a noisy and perhaps past-its-best 777 with ropey IFE would indicate the need for a good stock of fluids and snacks.