The key to any senior bodybuilding routine is to not overdo it. It's easy to fall into the trap of feeling like a young, viral 18 year old, but as a person's body ages things start to slow down. This isn't any reason to avoid cardiovascular exercise or senior bodybuilding routines, but rather a reminder to take things a bit slower than you would have a few years ago.
As we age, or metabolism slows down and sometimes our digestive system has to work harder to keep everything moving. Working your fingers to the bone in the gym, then eating like a horse to build muscle doesn't work as efficiently as men and women creep past middle age. After age 50, testosterone isn't nearly as abundant, which means overdoing it (when doing senior bodybuilding) is more likely to lead to injury, rather than stronger muscles.
Starting a program geared toward senior bodybuilding needs is the best way to avoid injury. Starting with a few simple exercises, spread out over the course of the week is ideal. Try starting out with a 1 on 2 off routine, where you work out on day 1, then take two complete days off to assess how your body feels. Also, each workout should be limited to 2 or 3 exercises, 2 sets each, with at least 1-2 minutes rest between sets to make sure your body is ready for each set.
Day 1 (perform 2-3 sets, 8-10 repetitions each):
Do some very light dead-lifts, or seated vertical leg presses.
Lightweight lying hamstring curls.
Triceps extensions on a cable machine.
Light bench presses.
Machine-assisted shoulder presses.
Standing bicep curls, or machine preacher curls.
Another rest period. Assess how you feel during this period, you may need extra rest, or feel like you can add some more weight in the upcoming week.
Adductor machine with enough weight that you feel a slight resistance
Lying abdominal crunches.