Dude, 34 is not old. I'm 37 with myopia, astigmatism and keratoconus, and don't have any problems using the tablet, even at night without visual correction.

Shimmering and headaches? I gather you've let other people look at the screen, and they don't have any problem? Otherwise, it could very well be a faulty backlight.

Anyway, return it, eat the loss.