Changing Systems font size

After a long time my dad has finally replaced his old PC for an iMac. As he is 50+ he asked me whether he could enlarge the systems font. I took on the challenge with quite a lot of confidence, being around Apple Products for the last decade. Sadly this was a problem I never had to cope with and after a long time I had to give up. As it seems there is no such thing in "the World's Most Advanced OS" that would let you enlarge the font and make the enormous 27" screen useful. Any ideas on how to make my dad's life easier? Maybe Mavericks soon?

Cheers

Luca