Being excited about taking psychology is a good reason to take psychology 
My son almost did not take a lab science in senior year. He was thinking about applying to business / economics, and a college counselor told him that it was not necessary to take another lab science.
At the last possible minute my son switched to a lab science (physics). And then he changed his mind about majors, and applied to engineering instead of business / economics. In his case, in retrospect, not taking a science class might have ended up closing some doors for him.
So, I’m just responding to what you said, that “he has not ruled out something in the health sciences.” I’m not an expert, but I would guess that Bio would be stronger for that path. On the other hand, it’s also important to take classes he’s excited about!