A good way to implement the moving up to the next age would be to make portals only accessible once you've unlocked them, and display a message to the player letting him know he can go through to the next age.
Another way is through a plugin like multiverse (although it would be extremely resource intensive for larger servers). You could make one world for each age, and each world has a special set of permissions that allow you to craft and use certain types of blocks, as well as making blocks not spawn in the world. For example, replacing redstone ore with stone in the earlier ages where redstone isn't "unlocked".
I think this is a fantastic idea and hope it gains support. That being said, I think I could possibly implement this RIGHT NOW on my server, albeit with a lot of hard work and tweaking. PM me if anyone is interested in working with me on it.
