Who said that trees don't get old?
This is Level 3 with one major modification - Dyson trees and defence trees are most fertile on level 2 and when they grow to the max, they are pretty useless.
So it's up to you, to build new trees when old trees become old or to deliberately surrender your asteroids to the enemy and then recapture them. Or just to run the seed rush.
It's more like a concept, so it may be quite easy. Please, report things that should be tuned.
Thanks again to Jamis for her, literally, text-book of parameters.