How does a 53 year old man outdo his workout plateau? He needs help, but wont really ask.?

the man i work out with is 53, a retired master chief and has been my instructor (guide if you will) and has helped me immensely with losing weight and gaining lean muscle over the last 15-16 months. today he told me that he is the exact same weight he was three years ago. he is concerned because he has a very healthy diet and a very disciplined workout and lifestyle. just so i can help him maybe think of whats wrong, could someone give me any kind of insight? i mean this man is extremely strong and strict with his regiment. he was a senior master chief in the navy and he is extremely disappointed in his more current results. he does drink a lot of beer and whiskey but he always has and at one point was building, now not so much. please any insight you may have would be great...