Four years is actually a significant runway, and inmates who use that time deliberately come out in a completely different position than those who let it pass. Start now.
Most facilities offer vocational training programs in trades like welding, electrical, plumbing, HVAC, culinary, auto mechanics, and similar hands-on skills. These are real certifications that translate to employment on the outside. Have him ask his counselor what training programs are available at his facility and how to get enrolled. Some have waitlists, so getting on them early matters.
Beyond formal vocational programs, reading is one of the most underrated tools available. I read hundreds of books over my time inside and came out sharper, more curious, and more humble than when I went in. Reading expands what you know, what you can talk about, and how you think. The key is following genuine interest rather than forcing a curriculum. What is he naturally drawn to? Business, technology, history, construction, cooking? Start there and let the interest carry him. Send him books on those subjects through InmateAid or Amazon. A person who reads voraciously for four years will be formidably prepared for almost anything.
Work with him to build a four-year plan: what skills he wants to have, what he wants to know, and what kind of life he wants to build when he walks out. That plan gives the time inside a purpose it would not otherwise have.