My age is 33 and on my watch I have a constant fitness age of 30. It keeps telling me that if I keep on track with everything I could lower it to 29. All my boxes are checked green for months.
Also my watch keeps throwing me tiny celebrations and report that my fitness age is lowering to 29.5, then it was 29 and yesterday it was 28.5 (yey!). All the time the Garmin Connect shows 30. I guess it's a bug, but even with new updates it won't budge. It's not a gigantic bug, but it's annoying when I try to actually do better and it just shows me bogus goals.