I thought I knew the mechanism, and recent tests proved me that I was wrong.
First question is : how does it work ? Does each nature magic level give the unit a % bonus to age limit ? I thought it was 30% (tested in CBM 1.92), then I happened to empower a precious unique hero recently in MP, and noticed a +51% bonus to age limit !
Before empowerment
After empowerment
Second question is : Is there a difference between vanilla & CBM about this ?