Mangekyō Sharingan is awakened by a person when he/she suffers the loss of their loved ones. The Mangekyō Sharingan provides a person with amazing powers. Also, it makes the person much more powerful. So, today I have made list about the characters who awakened their Mangekyō at a very young age.
8. Fugaku Uchiha-
Fugaku was the Uchiha clan leader and the head of the Konoha Police. He had awakened his Mangekyō after his friend died trying to protect him. This happened during the Third Great Ninja War and he was 34 years old during that time.
7. Madara Uchiha-
Madara was the first Uchiha to awaken the Mangekyō Sharingan along with his brother, Izuna. According to the Wiki, it was during adulthood that Madara awakened the Mangekyō. So, he was at the of 17 when he did it.