If you're behaving immaturely, someone might say 'grow up'.

如果你的行为很不成熟，别人可能会说“成熟一点”。

The entire process left me jaded, and I decided, immaturely, that I would never place my future in someone else's hands ever again.

整个过程让我厌倦了，于是我不成熟地决定，我再也不会把我的未来放在别人的手中。