Abhimanyu, son of Arjuna and Subhadra, was killed at the age of 16 at Kurukshetra in the Mahabharata war. He had entered the Chakra Vyuha (army formation) formed by the Kauravas and got killed as he did not have the knowledge to come out of the Chakra Vyuha. It is stated that Abhimanyu got killed at the age of 16 because of his previous birth.
It is stated in the Chapter 67 of the Adi Parva of the Mahabharata that in his previous birth Abhimanyu was Varchas, son of Chandra, the moon god.
A huge assembly was called by the Devas to decide on as to who all should incarnate on earth to help in the destruction of people following Adharma.
Chandra was not ready to allow Varchas to incarnate on earth as he did not want to be separated from his son for a long period. But he also did not want to create an obstacle to the grand design of the Devas.
So he agreed to Varchas being born as the son of Arjuna and return to him in the 16th year.
The Devas agreed to the condition set by Chandra and thus Varchas was born as Abhimanyu, son of Arjuna. He got killed at the age of 16 when he entered the Chakra Vyuha in the Kurukshetra war.