Out of interests, where has he applied to?
Some advice I was given at 17 on a short course at an art school was to make my portfolio reflect me and my interests, not show a range of skills/what you think they want to see. Even if that means a portfolio full of drawings of cliffs, or whatever: it has to be true to you, so you can defend it and discuss it passionately and sincerely at interview and in crits when at college.
That was the opposite of what my art teacher thought (he was pushing for heavy focus in life drawing, which I now know from my BA, MFA and doing some teaching at art school, would not have piqued anyone’s interest. I mean, some is fine, but you know what I Mean!). this was advice for Fine Art, not Foundation, though.
A foundation is a great idea if he’s not certain what he wants to do. He should look up the degree shows of some top schools. I would say that there are now more performative/not traditional fine artists doing really well in the contemporary art world, that may interest him and show that Fine Art doesn’t necessarily mean having to focus on painting rather than costume. Eg Zadie Xa.
Foundations are excellent for artists to develop, and I’d always recommend them, although I personally went straight to BA as was certain as to which area I wanted to work in.