Barring some cardiac condition (many of which can’t be detected without thorough medical tests), or an injury, age shouldn’t preclude him engaging in just about any sensible hard program. He will want to make sure he allows for good rest, as recovery becomes slower with age. He might also want to incorporate some pre-hab/balancing exercises in his routine to both counter years of developing muscular/flexibility imbalances and the higher potential for injury as we get older. You can do a search of the articles for pre-hab and renegade for some examples of these. He might want to consider some supplements to protect joint health, like condroitin, and heart, joint, inflammatory health like fish oil.
Other than this, which program to chose depends on his goals, and available equipment. He may be less enamoured of betting huge than when younger, and might be more focused on strength, flexibility, general fitness, or a number of other goals. Let the goals drive the choice of programs. Like all of us, sticking with a single program is not as effective as choosing several basic programs that stress different aspects of our physique and fitness important to our goals.
That said, he should probably start with a sound beginning lifting program emphasizing strength for the first several months as a foundation. Combine this with some pre-hab/balance exercises, smart flexibility work, some soft-tissue work (search under rollers), and some cardio, and he will be in much better shape in a few months and less suceptible to injury. While there are a number of solid beginning strength programs, I’ve leaned toward ones based on Rippetoe’s. It centers around a few complex lifts that target the big muscle groups and recruit multiple muscle groups in each exercise, a focus on strength (3 or 5 sets of 5 reps), an emphasis on learning good form, and the progressive weight increases. I’m sure if you search under beginning programs, you’ll find more on this and others.
Finally, he’d benefit from spending some time getting educated or refreshing his knowledge by reading the good info on sites like this.