I'm well past 60 and wear correctives lenses with bifocals. I like the Vortex levels because they are a large size. Mount them on the left side as far back as possible. Still, I had to break my cheek weld to view the level through the bifocal.
My solution was to adjust the height, cant and length of the shoulder pad and stock to conform to the shoulder pocket when the level bubble is between the lines. Get into position, pull the stock into the natural, comfortable pocket, and check the level. If one has adjusted the rifle to fit naturally into the shoulder and taken the steps to level the scope accordingly, it's amazing how close to level things are, even on a right angle incline. Check the level once, shoot.
Takes some dinking around and practice to get things set right but that's what worked for this old grump.