Why does Killua retake the hunter exam?
Because the hunter license gives him access and benefits that he won't get without it. You get a lot of free things and other services, less restricted travel, and sometimes an excuse for having killed someone. And some better opportunities for employment.
9 He Murders One Of The Other Contestants In The Hunter Licensing Exam. Killua kills Bodoro during the Hunter Exam, despite the fact that it's against the rules to do so. After stabbing him through the chest from behind, he is disqualified from the Exam, and he therefore fails.
According to him, he was almost 12 when he sat the first Hunter exam. As fans know, Killua ended up taking it again a year and a half later, meaning, he was 13 or 14 years of age at the time.
Illumi threatens to kill Gon if Killua even attempts to fight him, so Killua gives up and becomes silent for the rest of the exam. Killua murders Bodoro in the middle of his match with Leorio for no reason and is disqualified.
Killua passes the Hunter Exam on his second attempt and returns to the game.
The last rule known to the Zoldyck family is that the same person cannot ask Alluka for consecutive wishes.
Some believe he left Gon because he found what he wanted in life through Alluka. Others believe that his promise to Bisky was the reason why Killua left Gon. The truth is that both interpretations are correct; Killua left Gon because he found what he wanted in life and because of his promise to Bisky.
Age: 13-14 Years Old
Killua hasn't been seen in action since he bid goodbye to Gon at the end of the 13th Hunter Chairman Election arc, but fans can't wait to see him come back at some point.
Leorio joins the 287th Hunter Exam, becoming the applicant #403 and passed.
One of the reasons why HxH is such an entertaining series is the dynamic between the characters. For example, Leorio, Gon, and Kurapika pass the first phase of the exam by working together to save a man from falling overboard.
Why is Killua not taught nen by his family?
In short, Killua was raised as a killer first of all from a psychological and physical point of view, learning the nen before all of this would have simply made Killua less strong and, consequently, less suitable to be a killer.
Prior to the Chimera Ant Arc, Gon had never actually killed anyone, except some wildlife for food. Despite how coolheaded he's been with seeing death, Gon himself had never shown one murderous tendency before. He even inadvertently influenced Killua to stray away from killing for some time.

Silva Zoldyck (in Japanese: シルバ=ゾルディック, Shiruba Zorudikku) is currently the head of the Zoldyck Family, Killua's father, and an anti-villainous antagonist in Hunter x Hunter.
Character | Age | Birthday |
---|---|---|
Killua Zoldyck | 12 | July 7th, 1987 |
Kurapika Kurta | 17 | April 4th, 1982 |
Leorio Paradinight | 19 | March 3rd, 1980 |
Hisoka Morrow | 28 | June 6, 1971 |
10 Bloodlust & Intent To Kill Throughout The Series
This is a quality that villains often carry, and Killua was one of the few main characters who did it as well. Being able to flip a switch and get into a murderous state is definitely a point in his villain category.
Killua had been trained as an assassin by his brother to be extremely cautious that he only engages in combat provided that victory is absolutely certain.
The 288th Hunter Exam was held on January 7th, 2000, while Biscuit Krueger and Gon Freecss trained inside Greed Island. The exam site was in Beeskafmarro, Diksakura store (basement) by the station and the only graduating participant was Killua.
In short : Killua got hurt extremely badly during the separation scene, because to him, not only did Gon confirm his suspicions that he's only a teammate to him, but he also implied that he'd rather hurry up so he could meet Ging.
He was afraid Illumi might be able to get his needles in him again to control Nanika which would also hurt Alluka since they share the same body. Nanika and alluka are two separate beings. He nanika to never come out again to keep alluka safe from those who want to abuse Nanikas powers.
The reason is because Killua had never experienced the feeling of having a friend so imagine how it would feel if his first ever friend and him parted ways, and especially when he was raised differently then most plus to Killua, Gon is his sunshine.