I am in my seventieth year and my eyes are not good. Many paperback books had fonts so small I couldn't read them even with my glasses on. I don't have any problem with the Kindle. Never having seen the Kindle, I got the DX and that was a mistake. Shortly after I got it I saw a smaller Kindle and could read it fine so I'm going to try to sell the KindleDXG.
I tend to change the font size from daylight to night. If the light isn't excellent, I need to enlarge the font one click.