callow

This word carries a specific flavor of naive confidence. It does not just mean young; it suggests a lack of polish or a certain awkwardness that comes from not having been tested by life. It often evokes the image of a bird that has not yet grown its full feathers, implying a vulnerability and an openness to being fooled. While words like immature can be purely insulting or clinical, callow often contains a hint of condescension or pity. It is frequently used in literary contexts to contrast a protagonist's early idealism with their later, more cynical maturity.