Fitness age Calculations

I’’ve had my Garmin 165 for a few months.  Ive been looking at fitness age and trying to use it and lower it.  It asks me to exercise 3 times a week and average more than 75 vigorous minutes a week.  I always exercise 3 or 4 times a week and the watch is showing way over 75 mins of vigorous exercise a  week  - yes when I look at fitness age it tells me I am under number of exercises and vigorous minutes a week.  What  am I missing here?