The Torah in Breishit (Genesis) 34:25 describes Shimon and Levi when they fought against the city of Schem (some spell it Schechem) by the term איש (pronounced as, eesh) which means man.
Rabbi Dovid Ganz (writing in Prague, Jewish year 5352, or secular year 1592) does the calculation in his book Tzemach Dovid (on the Biblical year 2207) that Shimon and Levi according to Jewish sources were no more than 13 or 14 years old at the time.
Yet the Torah defines them as men, that is to say adults.
Judaism defines being an adult at a much lower age than the definitions used in Western Cultures.
So whatever you want to say about the Norway incident, keep out the issue that they were kids.
According to Torah standards they were adults.