Hey kimio221!
For the moment there is no way to gain new units, but also, there aren't any age related limitation, so what you've experienced is most probably a bug.
I've solved similar one in v0.12.5, so if you're already running it, please send me error log from "%appdata%/../LocalLow/Tazoru/SpaceArchitect"
I hope to add a way to get new units within a month, I'm also starting work on game save mechanism :)