first I think it would depend on the species (some live longer and some shorter), for a panther or vield I gather that around 12 months is considered adult so I guess under 12months would be sub adult? juiv maybe under 6 or 8 months (just a guess)
I would like to say anywhere from 1-6 months is juvenile. They're probably half way grown by 6 months so that's when I would consider mine a sub adult. Plus, they can start reproducing at 6 months sometimes sooner, but really shouldn't be bred until 12 months the adult age. Anyone else have any insight on this? This is how I have seen it.