On two echos, my EF was 58% and 80%, it depends on lots of factors, like
heart rate,
stress level, fluid intake, food intake, etc.. EF usually won't decrease with age.
3. I've never seen VO2 expressed in percent. If you mean % of normal (expected for your age), 53% is indicating that you are in really bad shape and should exercise more given that your doctor tells you to. Or you may have another disease that should be investigated.