I can not answer your question with any authority, but can share my experience.
I got RES last fall at 1" size and earlier this summer caught some by hook and line that were in the 4-5" range. I moved 4 of these RES from the pond they were in to a tiny pond to see if they would reproduce there. One male immediately made a nest and was guarding it. That was about two months ago.
That might give you a timeline on size of fish and age and ability to at least make nests.
