If he wants to be an accountant, then ACCA is one of the main recognised routes (although there are a couple of others) -however, any degree he does, even an Accountancy degree, won’t be enough for him to be considered a qualified accountant under the ACCA framework, at best he would be exempt from some of the early exams but likely he would need to continue studying post-degree for at least 2 years. It can be expensive to self-fund.
if he decides to lean in that direction, I would suggest he looks at post-18 apprentice opportunities. Many financial companies are offering these now, it means he would be earning a wage, his training/exams would be paid for (as long as he stays employed for a certain period - eg 3yrs, he would likely not have to pay this back), and he would be getting on the job experience, which for the ACCA route at least, they also need 3years of experience alongside the exam passes to qualify.
he might still prefer to go to uni first for the broader experience, in which case a variety of degree topics, including maths, accountancy, business management - all of which would have some use, and as mentioned earlier, would potentially exempt him from some of the early ACCA exams. If you are in Scotland, I believe there is less reliance on student loans etc, so this might be a good opportunity for him - if he was in England I’d strongly advise against uni because the weight of student loans for the limited benefit of the degree seems excessive at the moment.
edited to change Uk to England!