Metabolic Age???

Has anyone had this done at the doctor's or gym? I just turned 48, feel better than I have in years, and my metabolic age was 72?!?!? What is that?
Had it done at the gym with a BMI calculator, like a scale but you also hold onto handles while it send electrical pulses through your body to determine fat vs muscle, etc. Is it BS? Or am I a prematurely old lady?