When i joined a gym a few years back they not only checked my BP but measured my lung capacity. If your son is unsure about his fitness tell him to see his GP and ask him if he is fully committed to a gym.
When signing a contract for gym membership the minimum time is about 1 year so he has to stick it out or he will lose his money otherwise.
my local council-run gym takes a medical record (tick box sort of thing) and does an assessment on the treadmill to assess what level you should start at, if you've not been to the gym before.