When he starts his Phase 2 (Trade) training, which is more academic, and in his chosen role. Seriously.
It's military training; it's hard for a lot of people, no matter their age, but that's the point. The military ethos is warfighter first, job second, so they will push people physically and mentally to find the personalities they want, but that's not to say he won't have times in the future when he's working and he's tired, rubbish weather, lots to do, and that's when those first weeks carry across and you push through. It's a case of remembering that it's (potentially) only 10 weeks and eyes on the prize.