Hah, I just turned 72. I'm way beyond being able to finish a drinking project of that scale!
I'm fortunate in that I live at 5600' and am able to get into the high country pretty often. I've done several hikes this year in the area I'll hunt opening day (8-25) at 10,800' and have had no problems.
For someone who is coming from lower elevation without any experience hunting high, a can of oxygen is probably a good insurance plan. IMO, if you are up high and find you need it you should use it to get back down rather than try to continue the hunt. The secret is to move at a pace that you can continue at without frequent resting. Watch your heart rate and know what your low side training rate is and try not to exceed it. You will get there just as fast pacing yourself as you will pushing beyond a comfortable heart rate and breathing zone.
I see those cans of oxygen for sale at some of the gas stations in the mountains but I wouldn't count on finding it after you get to the hills.
So, my view on it is the oxygen should be carried and used as a part of your emergency/first aid kit. If you need it, use it to get back to safety.