re. heart rates, do your various heart rate thresholds stay constant, or do they vary depending on how fit and how much training you are doing? i.e. do you need to keep re-adjusting what your max and resting heart rates are, or are they set in stone?
IIRC your maximum heart rate does reduce with age, but not by a huge amount. Your resting heart rate will go up or down according to how fit you are. It can also be temporarily affected by illness for example.