Once Leon reaches 26 years old, a dragon is considered to have entered the teenage stage, meaning it has already traveled far on the road to adulthood. Although to truly reach adulthood, several more 26-year cycles are required.
Leon ran away from Mother Dragon's nest shortly after hatching and has no idea on which day he was specifically born. Even now, he's still a bit fuzzy and can only roughly guess his age, waiting for the day he meets Mother Dragon or Dragon Sister again to ask them when exactly he was born.
Therefore, Leon is merely guessing and assertively considers himself a teenage dragon now. After all, reality is not a game where different age stages have stark differences in strength. In reality, there's not much difference between a teenage dragon about to enter adolescence and a young dragon that has just entered it, and being off by a few months or a year isn't a big issue.
