Ten years ago in my early 40's I was getting a lot of injured joints, so I decided to change my training by pyramiding the weight upwards so that the last set for each exercise was the heaviest. This way I'm warming up for each exercise I do, and I don't need to do a general warmup at all before my workout.
I've had very little joint problems since doing this routine. An example exercise: Bench Press 120x8, 135x8, 150x8, 165x8, 180x8. This way you are increasing your weight used by 50% between your first & last set. I hope this helps some of you old guys like me.