I mean, growth spurts happen, and when they do, typically you increase height by a lot in a very short period of time. So I think it is plausible for Jing Yuan to go from his "teen" height to "full" height within the span of a single year. *shrug*

Also, if you equate his "teen" height as close to the current height that Dan Heng (who uses the male teen model in game) has right now, it's not that short/shota.