Seems like everyone has ideas for new ages. So it might be a good idea to talk about the design process and how ideas will become ages. Now individuals of coarse can proceed in whatever fashion they want on their own personal ideas. This is more for 'official' group projects. Here's what I was thinking would make a good process.
1. Idea. Whether through brainstorming or a forum post or whatever an idea is suggested.
2. Ratification. Idea is approved by the group as a possible project.
3. Refinement. A design document is created that outlines the goals of the idea.
4. Concept. A small team begins illustrating and creating the story for the age.
5. Level Design. A rough basic version of the age is created. All scripting and layout are done to ensure that the level will work. It is tested and refined until it works as intended and is fun to play. No detailed assets are created. It would be a waste of time to create assets for an age that either doesn't work or would under go revisions and be needing modification or thrown away all together. I know I would be pissed if I were to make a bridge only to have the river it crossed get axed and my bridge deleted.
6. Beautification. Now the detailed stuff is created for the age using the concepts from step 4. It continues until the group is satisifed with the look.
7. Submittal?. Hard to say what happens next.
So that's my suggestion for the design process. Feel free to revise, completely bash at leasure