Window -> Preferences -> General -> Appearance -> Colors and fonts.
In that small list of folders, choose
Basic -> Text fontand hit the change button. Tada! Kinda a lot of effort, but it will be worth it in assisting your eyes from squinting all day long.
And hey, while we're at it. If you are starting to type something in the code editor, but can't quite remember the whole variable name or whatever... hit ctrl+ spacebar. Flex will then make a suggestion. This is a very handy feature as well..