My site is only 1.5 years old. Revenue was stable that time. I think the biggest break was before that. But my site is also not "made for adsense" which was what google mostly penalized.
Its more like a forum, but not one. Users can post their own content and others can vote and comment that. Plus it has a huge searchable database.
The problem with static sites (i have those too) is that google loves site updates as often as possible. A site that is good ranked today can be killed by a more dynamic one next day.