Hang on a second. A while back you said you’d entered your sixth decade. Seventh, my dude!
Apologies for the digression, folks.
Which is agreeing with what I said. Your resting heart rate isn’t really affected by age, just by the volume and intensity distribution of the exercise you are undertaking at that time in your life. Though I’d put a caveat at 16-19 as you are still growing at that stage.
My point was that age doesn’t drive changes in your resting HR, exercise does. Maybe that wasn’t clear in my post you were responding to?
But that isn’t what I was trying to say. I was a very active runner and super fit. I stopped activity due to illness and restarted at 55. My activity to get me back to being fit resulted in a drop in resting heart rate. i was young and fit with a high resting heart rate. I end up old and fit with a low resting heart rate
Very similar numbers for me over the last year, with the same cause and the same results of 80s to right around 60, and floor and ceiling have moved up a bunch in the last 6 months with much fewer outside (nonstructured) rides. I’m 53 now.
Age: 36
Resting: 39
Max: 202
Range: 164
I can reliably hit 200+ on the trainer but outside I haven’t found a reliable place to test this. When I go camping or on a vacation to somewhere out of the city, Garmin sometimes records a 32-33 rhr with periods of no recording. (Do the watches detect under 30?)
Did you do a lot of easy Z1/2 runs when young?
Unlikely I did.
But I also didnt do easy cycling until the last few years. My heart rate had already gone done by that point.
The lower intensity rides are what bring down the resting heart rate over time as they are the ones maximally increasing stroke volume. Understandable resting would be higher if you haven’t been doing these to any great extent over time.
I get the theory. I just can’t apply it to myself
41
Resting 29-34
Max 192-194
Range 165-158
Notes: resting depends on quality of diet/sleep, and I think how low it gests s mostly genetic. My 70 year old father, who does a lot of low intensity activity (hiking, walking, biking) tells me he still has his resting HR drop below 35bpm sometimes when he’s just woken up, which is usually a 30sec of full minute manual count.
33
Resting: 43
Max: 172
Range: 129
We’re similar 
Age 47
Resting 50
HRMax 192
VO2Max 72 (lab tested)
Awesome VO2max 
Im the same age and I have not hit that for several years (and it is Garmin tested, so take it with a ‘Pinch of Salt’).
Age: 33
Resting heart rate: 28 when fresh, but normally around 35
Max heart rate: 198
Heart rate range: 170
Garmin VO2Max estimate: 58
I think it doesn’t work for people that have a super low RHR that is not mostly due to training adaptations.
Also, some trained people don’t update their max HR and keep anchoring to the max they saw a long time ago. It has to be a moving window and it requires very, very hard efforts.
Your implied Vo2 vs Garmin seems very off
Daily RHR is calculated using the lowest 30 minute average in a 24 hour period . 7-Day Average Resting Heart Rate: Some watches will display a 7-day average resting value which is the daily average resting heart rate over the last seven days. It is a rolling value and does not reset at the beginning of each week.
When I look at the graph I’ll see several readings under or near 45bpm but it’ll report nearer 50bpm. I think that 30minutes doesn’t have to be continuous though. A few times I’ve had a reading say around 50bom, took a quick 5 min shower in the evening with the watch off and somehow its continued to read stupidly low bpm and that has brought the average down 
The most telling “proof” of the range as proxy for vo2 is how it expands at sea level.