I tend to do better than most at high elevation, so I'll toss in a few words on my experience for comparison.
I'm 63 and I have been playing in the mountains for 25 years. I live at 5,000 feet, which is clearly an advantage, but I think it's a small one. I get above 10,000 feet nearly every week and have never had any symptoms except mild Cheyne-Stokes breathing on Denali. I never take extra time to acclimatize, but I try to sleep as high as possible (usually at the trailhead) before climbing. It's common for people to kick my butt at relatively low elevations and then watch me return the favor up high. Some might say that I'm perpetually acclimatized, but I still felt fine when I have gone up high after several months away from the mountains. I think I'm just one of the lucky ones.
Having said all that, I've only used a pulse oximeter once at altitude. Saturation was 93% about five minutes after reaching the summit of Middle Palisade (14,040). Pulse was in the low 90s. We had slept near Glacier Lodge the night before.
