Based on my own experience (at age 60) when we did volunteer work in New Mexico (above 6,500') it took me a good 10 days to acclimate. Even then, everything I did was slower than at sea level. Today we live at 4,500' and I never noticed any difficulty.
How quickly you acclimate, if you ever do, depends greatly on your state of health. If you have heart problems or respiratory problems, altitudes above 4,000' may not be recommended. If you have health difficulties, check with your doctor before you make that trip.
Paul <?)))>< Lake Almanor, CA
2002 Thor Tahoe 23FBGL TT, 28'