User blog comment:Pigzillion/How come Killua learnt Nen so late?/@comment-5780397-20150809010956

My guess is that the Zoldycks are taught Nen around Killua's age, or maybe a few years later: afer all, it is a dangerous ability, though I am saying a very stupid thing, since they electrocute their children. The only reason I can think of is that the traditional training specifies a certain age, since we don't know how Kalluto learned it.

Or the training might differ from children to children: Killua's training is more physical and battle-oriented because he has shown predisposition in those fields, Milluki is a failure of a fighter and thus focuses on engeneering and hacking, Kalluto is not too strong by the Zodiac standard but was thought to be exceptional at Nen... Who knows.