Generally speaking, athletes have lower RHRs than the general population. [Similarly, athletes generally have higher MaxHR (i.e. the 220 formula is too low; other formulas yield from 3-12bpm higher.)
However, better HR-based endurance metrics include the rate at which you can drop your HR from FTHR to endurance, and decoupling factor (Pwr/HR for successful intervals). I think these latter 2 metrics would be better to follow in preparation for riding at altitude than RHR.
my max is 179bpm aged 53 - so a range of 35-179…so not a big range. That said in my 20s when I did triathlon my resting was 36 and the max 196 so a bigger range…if that made a difference…who knows 
I will add some metrics to this:
44 years old, training for 1.5 years, before I’ve not done any endurance sports since I was around 21 years old, only strength/power lifting.
My RHR dropped from high 60s/ low 70s to around 48-50bpm currently. I’m seating and typing now and it’s 50bpm. I always had lowish blood pressure. As for my max HR, I’ve hit 210pbm last summer on a hot day. I can usually get to 200bpm when doing vo2max intervals if I push myself really hard. Also if I’m not recovered well enough, my HR will not get to those levels.
Also my vo2max according to garmin is 60.
Mine was already in the 40’s without doing any real cardio (just went to the gym from time to time). My brother and nephew have the same but they can hit higher max. HRs (upper 180’s/lower 190’s), my grandfather had it as well but the generation in between (my mother, aunt and uncles) don’t.
Over the course of 5 years of triathlon training, I’ve seen it go down to 34 while lying on the couch to watch the Spring Classics whilst I was still wearing my HR strap. No idea how low it might be when I wake up.
I’m 29y/o and the highest heart rate I’ve recorded is 177 so probably just a large “pump”. FTP >4.6W/kg (avg. HR during 20’ was 164 and max. 171) and VO2Max from an INSCYD test was 71 for cycling, Garmin estimates 72 atm. Ran my best 10k yesterday in 40’32" at an avg. HR of 166 and max. of 171 as well. Last running VO2Max was measured at 62 via an Inscyd test, Garmin estimates 59 atm.