Be careful adding it to your regime your workouts are meant to build strength the byproducts of this should be increased flexibility, bone density, metabolism and for an older trainee (which you think you are) tendons actually become stronger and thicker for which explains (old man strength).
Your recovery at your age is paramount my suggestion for you is to incorporate the aerobic component into you workout or alternatively get in the treadmill or stepper directly after a workout, hill-sprints would be better