Although some light has been shed on dragons in the show, it still seems like much of these creatures is shrouded in mystery. This season we learned that they are ruled by the Dragon Lord (currently Princess Ember). The dragons obey the Dragon Lord. An earlier episode showed us the dragon migration, and we found out that most dragons are not like Spike; they are mean to ponies. The traditional dragon lore also seems to hold true. Dragons in the series love hoarding treasure and they even eat gems. They are also generally shown as scary monsters with no manners.
But how exactly do they age? We see Spike, and though he clearly several years old, he is still considered to be a baby dragon. He is smaller than other dragons, and only about half the size of most ponies. Yet, in “Secret of My Excess” we see Spike grow in size as he becomes greedier. It could be possible that dragon development is tied to certain characteristics, such as greed or meanness.
The large dragon in “Dragonshy” hoards lots of treasure. Is it his greed that made him grow so large? Is it the disrespect he treated Fluttershy’s friends with that aided in making him so large? The world may never know.
“Gauntlet of Fire” shows us Ember, who is told that she is too small to win the Gauntlet and become Dragon Lord. Through her teamwork, understanding, and good morals, she is able to beat the others and become Dragon Lord, although at the beginning of the competition she tried to use brutish tactics like the other dragons. The fact that Spike and Ember are both small could be to show that they lack the unrefined qualities of the rest of their species.
Even if physical aging is not tied to their traits, developmental progression could be. Spikezilla may have been the same number of years, but there is no doubt that the dragon looked older. Many of the teenage dragons in the show are large, but nothing compared to the massive beast who reigned as Dragon Lord before Ember.
Feel free to share your opinions on whether or not you think certain “dragon-like” characteristics influence a dragon’s progression. Since there was already a dragon episode this season, I think it will be a while until more on the species is released. For now it is just overthinking time.