More Reps, Less Weight
It is a philosophy I completely agree with. I hear of middle-aged men tearing tendons and having ACL issues; all due to too much weight and jerking their weight s around while doing a circuit. I almost think machines are better for older men because you can manage the motion better.
This is a good read with some pointers for middle-aged men.
P.S. – I am not 60, but these tips still apply!