Great, brother. I'm glad that my advice has helped you and glad to hear that it's inspiring the old man. The healthier he gets, the better his quality of life will be, into his 60's and 70's. As I'm sure you're learning, diet is crutial. I believe it is not only the key to getting huge, but also the key to longevity. He may not need to eat the same cals that a bodybuilder eats, but the approach is the same. The diet alone will make a world of difference. 

As we age, our natural hormones decrease. For an older guy, it can get harder and harder to make progress if he is hypogonadal. I would suggest he goes in to have lab work done and see if he qualifies for HRT. If he needs it, this can make all the difference in the world, if he is motivated to eat right and train. HRT alone, without training and diet, may make him feel a little better, but just like using steroids without putting the work in, the results will be minimal. I am close to an older guy, that understands what I do as a competitive bodybuilder. Believe he is in his early 60's. He went on HRT about a year ago. He doesn't train and eats less than the 105 lb bikini girls I know. He came to me, frustrated and said, "I've been taking this test from the Dr for a year now, and I don't really notice any difference in my strength or muscle mass." I had to hold back from rolling my eyes. Point being, HRT can be great, but without the rest of the fitness plan in action, HRT isn't going to make a dramatic change. 

Some Dr's do put guys on HCG as their sole HRT program. It all depends on the Dr and how the individual responds. Before he did anything though, I'd see what his blood work says. Another great option, whether he qualifies for HRT or not, is HGH. 2iu ED is a good dose for rejuvenation therapy. Older guys usually show more dramatic response to 2iu, than younger guys that are already producing a decent amount of growth. 

If you check the Naps site, I am hosting "Project Get Shredded". The two of you should consider entering, if you have the time and motivation. If you do enter, be sure to note that you are together. That way, if you are randomly picked as one of the winners, I will take you both.