Yes, age is relevant here, also in that the middle-aged and elderly (as for example your cinema foyer couple) are less familiar with the conventions of device use in public than the young, who have grown up with it. On public transport, which I ride every day, the only intrusive conversations I ever hear are from the no-longer-young.Of course, the shyness of adolescence also plays a part in this, but also the near universal switch among the young to silent programs like WhatsApp for communicating.