As you age, your eyes will presbyopia. This means that for people in theie 40s or older, the computer screen gets a little fuzzy, even with glasses. Trying to read  fuzzy screen can give you a headache.

Where do the other aches and pains come in?
These are often caused by trying to read the screen through the bottom portion of bifocal or though half-eye reading glasses. You tip your head up or leanforward to see and this unnatural posture makes you sore.