How old is gon and killua

13 at the end of the anime, if you go by the official birthdays (Gon's birthday is May 5th and Killua's is July 7th). The Hunter Exam takes place in January each year.

*During the first Hunter exam (January), they are 11 (Gon states his age as "almost 12")

*When they go to Whale Island after Heaven's Arena (August), they are 12

*When Killua passes the next Hunter exam during Greed Island (January), they are 12

*When the Chimera Ant arc concludes (August), they are 13

Since the end of the anime, there was a 1 year time skip with another Hunter Exam to prepare for the voyage to the Dark Continent. So in the current manga, they have been offscreen 1 year and are 14.

Is killua Gon 12 or 14?

Similar to his best friend, Gon, Killua Zoldyck was also 12 years old at the start of his journey.

Is Gon a 14?

Anywhere Between 12 & 14. Gon is around 12 years old during the Hunter Exam arc, having been born on May 5th, 1987. His age can be extrapolated from several events in the manga, the most important of which is that the Hunter Exam takes place in January 1999.