When I was in my 20's I trained 6 days a week, now in my late 40's that would put me in the hospital. Here is my current routine:
Day 1 Chest/ back - 12-15 sets for each (shoulders cannot handle flat bench presses and dips anymore).
Day 2 off
Day 3 Shoulders/arms - 10-15 sets each.
Day 4 off
Day 5 Legs - Squats, leg press, extensions, leg curls, stiff leg deads... about 30 sets total... it wipes me out.
Day 6 off
Repeat
Getting old sucks, especially when you're a natty. I avoid super heavy lifts under 5-6 reps. If I feel any strange pain, pull or strain I stop immediately. Heavy singles are for guys in their teens and twenties.
If you take care of your joints you'll be able to train well into your later years.