Is this a praise of Joseph, a criticism, or simply a statement of fact?
Taking the third possibility first, we could argue that the Torah is simply telling us that when Joseph was a youngster, he spent time with his contemporaries, his half-brothers, the sons of Bil’hah and Zilpah.
If na’ar is a criticism, it suggests – as Rashi says – that he was cavorting and showing off in an immature way, getting up to mischief and unconcerned about how this would impact on his family.
Sforno offers another example of this approach, saying that he had not yet learnt how to control his tongue and involved himself in telling tales about his brothers and disturbing the harmony of the family.
The positive view sees him as a steadying influence on the sons of Bil’hah and Zilpah, trying to mould them into sensible young men with a good feeling for religion.
Years later, all this was past and he became a sound-thinking adult who was able to occupy a high position in Egyptian society with flair and vision.