The Garmin uses your calendar age in calculating your Fitness Age, so I would assume it does so in calculating your recovery times as well as a bunch of other measurements/values.
I don't agree with this process, though. If I'm 59 years old (which I happen to be) and in better shape than a sedentary 30 year old, why is my Fitness Age "older" than his?
I guess what I'm saying is, your calendar age doesn't (or at least shouldn't) matter. Your recovery time is whatever you need it to be. If you feel like you're recovered but the Garmin says that you're not, are you skipping your workout? If you feel like you're worn out but the Garmin says that you're fully recovered, are you running to the gym?
I wouldn't view any of these values as Gospel. They're helpful in a general sense, but they're not infallible.
Garmin seems to overestimate the recovery needs after high heart rate training, and underestimate the recovery needs after long workouts. At least that is how it is for me, who has fast twitch biased muscles.
