Fitness Age

In order to calculate Fitness Age, Connect uses a number of metrics, including weight (BMI), Vigorous Activity (days/week and minutes/week) and resting heart rate. From experience, the lowest age it will report is Actual Age minus 10. If you aren't wearing the watch constantly then you are not giving Garmin all of the information needed for the calculation. In this case, you'd be better just to ignore it. 

2953132 said:

This morning's run, like virtually all the others, was 8.04 miles,1:23:21 including breaks, av. heart rate 140 bpm, max 150 bpm, VO2 Max 42, 10,170 steps, on and on

At newer models, including the Fenix 6, the VO₂max value and performance in general are unimportant. VO₂max was used at older models (could be the case with Fenix 6 too, if you did not update the firmware for several years).

The currently employed method uses the following factors for determining the fitness age, as it is finally also shown on the respective screen too:

• Vigorous Days
• Vigorous Minutes
• Resting Heart Rate
• BMI (or Body Fat% if you are importing it into Garmin Connect)

I do not know how the other factors look like in your case, but for example the BMI at 6' and 190lbs is 25.77 which is already in the category 'overweight'. If you have low body fat%, and the high BMI is caused by high muscle volume, you should consider regularly importing the Body Fat% into Garmin Connect. If not, work on losing some weight.

And since you do not wear the watch 24/7. it is rather likely it does not measure your resting HR, and that this value is rather high, hence influencing the fitness age too. And in the consequence, the Intensity Minutes will be also rather low, if the detected Resting HR (RHR) is high, since by default the IMs are based on the ratio HR/RHR.

I recommend looking at the details on the Fitness Age page - it shows where your reserves are. You better keep the watch on 24/7. Personally, during the sleep I wear it on the ankle - I find it less disturbing, and it avoids getting a skin rush otherwise common if you wear the watch on the same wrist all the time.

When all factors are met, the table should look like this:

The older you are, the deeper the fitness age can go. I have it usually 9 - 10 years lower than the true age, but for example @gaijin who is in his 70's, got already 12 years less (or perhaps even more, I do not remember exactly). 

More information at What Does Fitness Age Mean in Garmin Connect? | Garmin Customer Support 

I'm in my 70's and my fitness age is 17 years less than my actual age.

Right, thank you for this.

Thanks for the response. I think you're right about keeping the watch on. The Fitness Age page shows a Resting Heart Rate of 122bpm, but that's because I take the watch off right after a run. I left it on overnight and the bpm was around 48. And thanks for the body fat import tip - always had muscle, always had poor BMI!

I'd agree it's not wearing the watch 24/7 that's skewed your fitness age. But, your runs all sound pretty slow and easy (maybe I've messed up the conversion to km), is it worth doing something different for one run a week?

I'm 60, and Garmin FR935 thinks my fitness age is 20 (it's very wrong!) I'm also a bit overweight and run 3 times a week for about 20% less distance, but with an average pace around a minute per km quicker, and heart rate anywhere from 140s to 180s depending on how hard I'm going, with a resting heartrate around 55.