Does he actually want to work in accountancy afterwards? Because if so, no, do not do a degree first. All it will do is delay him qualifying and being able to do the job he wants to do and leave him with a shed load of debt.
Even if you have a degree you still have to spend 3 years training and studying and doing professional exams to qualify as an accountant. Having a degree first is incredibly pointless unless you're hoping to get your first job in the a big 4. Even so, once you've qualified and proven your ability nobody cares whether you have a degree as long as you have an accountancy qualification and relevant experience. You can only work as a book keeper without one. Degree or not.
If he wants to do accountancy, then just get a training position. Employers will train you and give you time off to attend college and sit your exams (and pay for the courses). So after 3 years you qualify without any debt (unless you leave the job early, most require you to stay 12 months after your last exam) and experienced in the career path.
ACCA, ICAEW, ICAS, and CIMA are the routes to being a qualified accountant. If he wants to work in industry, then CIMA. If he wants to work in practice, then any of the first three. If he thinks he might want to do both/move between industry and practice or set up on his own, then ACCA.
Don't waste time on AAT unless he doesn't meet the entry requirements for ACCA/ICAEW/CIMA. I know ACCA have a mature student entry route but I can't remember the age. Check the website. AAT only gets you technician status - if you want to be a qualified accountant (able to call yourself a chartered accountant) you still have to do ACCA/ICAEW afterwards. It just extends the number of exams and length of time to qualify.
If he does ACCA he can start studying for it before he finds a job. Getting a few exams under his belt would strengthen his position when looking for a training contract and would confirm it was the right path for him. Although obviously he'd have to finance his own studies and exams. But it's basically pay as you go for whatever you study for. The fees are nothing like as high as for a degree. (BPP and Kaplan provide training and study materials.)
Advantage of doing ACCA is that he could do a degree at the same time, so by the end of it all he would be a qualified accountant and have a degree. Accountancy qualifications are reasonably marketable, and there are lots of different specialist paths you can go down after you qualify, if you so wish.
If this is what he wants to do he needs to do his own research. Employers will expect him to know about the qualification he's proposing to do, the exams required, the practical experience requirements, and the field he wants to work in, what the sector is like, that it's more than just number crunching, etc.
The people who want training contracts but don't even know the name of the institute their potential qualification is from, who've never been on the website, don't have a clue how to register as a student, or what the requirements are to attain membership... Well, they don't impress employers.