Just remembered that since Essint is a subjug purple, she’s maybe technically older since she’s gonna live for damn long time. Though I guess it depends on how one views troll aging.
Personally, I trend towards more arthropodic or hemipteran biology (bug/true bug) so trolls don’t really get into senescence the way that humans do. They are born as wigglers, pupate into young trolls (light grey skin, grey irises, not as hulkingly huge), and then hit a second semi-pupation and molt into full maturity where their skin is (dark skin, filled in eyes, full body size).
So it’d be egg, first instar as wiggler, second instar as young troll, ‘true’ pupation into adult maturity (imago). I’m not saying adults don’t age. They just don’t show signs of aging associated with humans.
There would be very little variation in terms of transition times. The variety of ages comes after the full molt; trolls would have equal time to develop in the eggs, hatch as a wiggler, and hit second instar after 2-3 sweeps. They spend most of their time as young trolls, but as we go higher in the caste the long lifespan the adult stage can expect.
We can assume that 6 sweeps is still considered the 2nd instar given the Beforus trolls not being pitch dark. The lowest caste are stated to live at most 24 sweeps with a minimum of 12. So unless the Empire is recruiting trolls who have yet to reach maturity, full molt has to be sometime before 12 sweeps. So I’m favoring 9-10 sweeps for full maturity? There’d be some variation due to enviro/genetics because that’s how variation works, but I’d like to think that these rough averages hold.
(I’m always open to discussion and interaction with these thoughts if any of y’all wish!)