preadolescent
The German word 'vorpubertär' is an adjective that describes a child who has not yet reached adolescence. It is often used in the context of child development and psychology to refer to the period before the onset of puberty. This term is used to describe the physical, emotional, and cognitive changes that occur during this developmental stage.
My little brother is still prepubescent.
This sentence points out a stage of development, and would be used to indicate an age or maturity level in context.
Simon behaves prepubescently, even though he is already 15.
This is stating a personal observation about an individual who, despite being of an age where certain behaviors would be expected, he still is acting in a way that is more typical of a younger, prepubertal child.
The prepubescent phase can be a challenging time for many children.
This is a more general statement about the stage of prepubescence, and it is expressing the idea that this can be a difficult transition period for many young people.