There are two ways, but I think the best for your purposes would be to
go into the Main Safari menu, top left, and select "Preferences."
Under "Advanced" make sure Universal Access is checked.
Then change the "Never use font sizes smaller than . . . "
to an increased font size. If it's 11 now, try 12 and 14 to see which one works better for you.
This will make both the fonts on your screen
and the fonts printer out larger.