I'm 69. About 5 years ago I put my Yamaha XP-225 in the back of the pickup and drove out to Silverton, Colorada, elevation 9500'. I met up with 8 fellow XP-225 owners and we road the high passes for a week. They went up to 13,000 feet. The continental divide crosses back and forth over the mountains there.
The only problem I noticed when I first got there and was unloading the pickup and putting stuff in the camper cabin was shortness of breath. I would have to stop at two loads, sit down and recover. But I acclimated in one day.
Riding my dirt bike requires a little strenuous activity, so I'm sure that contributed to my getting acclimated quickly. On particularly strenuous sections I did notice a little shortness of breath. But not much, a couple of moments put me back to normal. No lightheadiness, just a little shortness of breath.
One couple complained, cut their week short and went down to lower elevations. Younger than me by 10 years or so I think. So it depends on you mostly. Try it and see.
The next week we drove up to Moab, Utah in the desert at lower elevations and met with other XP-225 owners to ride the desert. I prefer Colorada much less dust.
Anyway for me, with a desk job back home, at 64 YO, I acclimated rather quickly.