User blog comment:Pigzillion/How come Killua learnt Nen so late?/@comment-4828844-20150809015327

I somehow agree with Martial. Since Killua is the prodigy, Silva and Illumi trained him thoroughly in stealth, combat, etc. They are taking their time to perfect his training. Once Kil mastered all these trainings (probably), he would eventually learn Nen.