For starters the best thing he can do is
1. start using sunscreen to prevent future hyperpigmentation (it will happen otherwise)
2. Treat hyperpigmentation with brightening cream or spot treatment (he should NOT go lighter than his natural color, just try to even out the skin tone to be like when he was a child.
3. he can visit a dermatologist that can provide honest advice and treatment. The 10k for the visit is worth the advice he will get.
4. remove stains from teeth with a teeth whitening kit (yellow teeth are true sign of age on people)
either pharmacies will have some of these products or there is a site called shopaviva that sells a few of them.

Just so you know also, the best way to prevent shaving issues is to use a new rasor as much as possible.