Medical student here. Would recommend a gap year 100%, assuming that he can defer his place. A medical degree can be fun, but it’s mostly just a grind and (depending on the course) there’s often relatively little opportunity to take time off compared to students on other courses. It’s not that it’s harder than any other degree, it’s just that you have lots of things to go (lectures, teaching, placement) and the holidays tend to be much shorter.
The next opportunity he’ll get to take a longish break is after FY2 (that is, after having worked for 2 years after graduation). Realistically, you can’t take a break after the 5 or 6 years of med school before starting work, partly for financial reasons, partly because it makes the first year as a doctor (FY1) that much harder. It’d be much, much easier to slot back into first year of medical school – where he’ll basically go over a lot of A level stuff again, so it won’t disadvantage him to be a little rusty – and there is considerably less pressure.
After FY2 he’ll have a bit more freedom, but that’s at least 7 years away.
EDIT – I did a gap decade (started med school when I was 30) so I may be biased.