Sorry, I meant to respond to that directly, I guess it got lost in the shuffle.
One of the points I made responding to
DomWolf, was meant for you too, which was that we seem to be using different definitions for Juvenile in the context of creatures like this within stories like these, in that I meant Juvenile to mean a fully developed body but underdeveloped mind/skills (on reflection Tween might have been a better choice of word), in terms of dragons that live thousands of years, anything under 300 might fall under this category (with 500-600 years maybe being young adult) (just pulling numbers out my ass).
With any long lived (intelligent) creature having a "childhood" lengthened proportional to the expected lifespan (aka elves under 100 in some books being classed as children despite being fully mature physically).