More than any other O.C.C., the druid's abilities increase dramatically with experience and maturity. Going up in druidic experience doesn't work on a strict time-scale; after all, a clever apprentice will learn faster than a dull one. As a character gains experience levels, his knowledge of druidic matters increases. After each level there is a test of some kind to check that the druid is qualified to advance to the next level. These tests differ from area to area and from druid to druid, so Game Masters should feel free to create their own.
Any player who has a druid for a character is assumed to have already spent years of study as an apprentice to an older, fully-qualified druid (only full druids may take apprentices). The character starts out at level one knowledge and ability.
The bold part is the important bit. I don't know about y'all, but I always read that as being an externally administered test... you needed to find another druid and have them test you. But, looking back, that's not what it says... just that each druid WILL face a test, and that the druid's test will be unique to them.
Which doesn't do a whole lot, but does make the class a lot more playable.