Pokémon needed time to grow naturally. Although Trainers could help them grow, that help ultimately had its limits. In the end, a Pokémon's growth still had to follow the laws of nature.
So when Chu Xin told Aier that he wanted Xiao Wu to evolve into Dragonite, she instinctively refused. As a resident of Dragon Tamer Island, Aier knew very well how powerful Dragon-type Pokémon were. But that power came with limitations. Their strength was bought at the price of vulnerability in their youth. Adult Dragon-type Pokémon were incredibly strong, but most were very fragile when young. They needed a long time to build up energy for their later growth. Only once they had accumulated enough power within their bodies could they smoothly evolve into their adult forms.
This was a natural restriction, as well as the path of natural evolution for Dragon-type Pokémon. Although most young Dragon-type Pokémon were weak, this period of buildup was essential. As they accumulated strength, they also developed their physical fitness. Without enduring those hardships, they would grow up weaker than others of the same species.
The most obvious example was Ash's Charizard.
That was why Aier felt so helpless when Xiao Wu brought up the idea on his own.
Aier reached out and stroked Xiao Wu's head. Although he was determined, she still decided to explain things to him so that he understood the drawbacks of evolving early.
"Xiao Wu, you need to understand that you aren't old enough yet. You're still young. There's no need to deliberately evolve into Dragonite just for a short-lived boost in strength!"
After Chu Xin explained, Xiao Wu understood Aier's words. Hesitation flickered in his eyes. He knew she wanted what was best for him, but he really wanted to become Dragonite!
Xiao Wu's desire to become