One thing to keep in mind, as we age it's tough to "add" muscle. Your T and GH levels begin that downward spiral around 30. At fifty they are just a fraction of what they once were. So it's not so much adding muscle as it is retaining it. Most weight programs will help us with that. Lots of good ideas above, compound exercise, adding a compound exercise to S&S, carries, crawls, and getting up and down.