Ha, I recently (about 3 months ago) got my Dad into lifting too. It’s been fun, and, haha, interesting…
Here’s my tips:
Basic diet, meat, fruits, veggies. If he can’t handle low carb, throw some potatoes or rice at him once a day around training.
Training, start with bodyweight movements, a lot of them, progress to barbell movements when he starts feeling bored or like his progress is stagnating. A heavy dose of push-ups, pull-ups, squats, lunges, and various conditioning (Sprints, Hill Sprints, Jumps, etc.) will get the results that most people are looking for at that age. If he gets in to it and his joints start feeling better, then by all means start incorporating some pressing, rowing, weighted squatting, etc.
As far as supplementation, Fish Oil is the only real MUST HAVE, at least imo.
If you feel like going further than that, I can’t recommend MAG-10 highly enough, a pulse or two each day has an almost magical effect on muscle growth, fat loss, recovery, energy, hunger, etc.
It’s a great product, and has become a cornerstone of my diet.
As far as the test goes, a diet high in healthy fats and protein should help out, as should training, but at his age it couldn’t hurt to get checked out.
The biggest thing for me and my Dad was he didn’t want to look “weak” in front of me, so he’d be stubborn a lot in the beginning. I just had to hammer it into his head that the only thing I consider “strong” is a consistent dedication to improvement. Now, it’s like every other day I look forward to training my Dad, it’s a really cool experience and I feel like I’m finally getting to actually know him as a person, not just my Dad. Plus he says he feels better than he did in High School, so that’s pretty cool.
One last tip, it always jacks my dad up when he thinks he can’t finish.
When he says he can’t keep going, just ask him how long he wants to be able to pick up his grandchildren someday, I guarantee he’ll get going again.
Good luck man, training family can be pretty stressful sometimes, but it’s a great experience when you can get them into it.