INTENSITY: Unlike anaerobic training (High Intensity to Maximum effort e.g Sprinting, Burpees, Mountain Climbers, etc) aerobic exercise dose not have to be at maximum in order to have a maximum training effect. A rough guide to training intensity is found by adding 25 to the athlete’s age, and subtracting that from 220, to give an approximate training pulse rate. e.g a 40 year old, plus 25 =65 and minus 220 would equal an aerobic training pulse rate of 155 beats per minute.
NB Aerobic training does not need to become anaerobic over the final stages, i.e. the pace should be maintained equally over the work period without necessarily ending in a sprint.
SUMMARY: Regardless of age, if you are in training for an event like a 5 or 10k run, or a cardio fitness test, a mix of regular aerobic and anaerobic training (like what you should find in a good circuit training class) will improve your cardiovascular endurance.