Having been a veteran of numerous battlefields since the age of 9, Guts (Berserk) is a extremely formidable mercenary and warrior.
Toshiro Hitsugaya (Bleach) was able to graduate from the Shinigami Academy in a single year with the highest written and performance scores in each of his classes and to ever reach the rank of captain.
Ichigo Kurosaki (Bleach) became a Shingami at age 15, while still a teenager his astounding growth rate allows him to become one of the strongest Shinigami, surpassing even most Shinigami Captains.
Kenpachi Zaraki's (Bleach) potential as one of the strongest Shinigami was prominent in his boyhood, allowing him to kill hundreds of outlaws...
...and defeating captain Retsu Unohana, the supreme master swordswoman, who believed Kenpachi potential was stronger than herself.
Despite being a high-school student, Prince Akatsuki (Choujin Koukousei-tachi wa Isekai demo Yoyuu de Ikinuku you desu!) is the greatest magician in the world.
Despite being a high-school student, Ichijou Aoi (Choujin Koukousei-tachi wa Isekai demo Yoyuu de Ikinuku you desu!) is the strongest martial art master in the world.
While still a high-school student, Kanzaki Keine (Choujin Koukousei-tachi wa Isekai demo Yoyuu de Ikinuku you desu!) is the finest doctor in the world.
While still a high-school student, Sanada Masato (Choujin Koukousei-tachi wa Isekai demo Yoyuu de Ikinuku you desu!) is the most successful entrepreneur in the world.
While still a high-school student, Ooboshi Ringo (Choujin Koukousei-tachi wa Isekai demo Yoyuu de Ikinuku you desu!) is the most brilliant scientific genius the world has ever known.
Sarutobi Shinobu (Choujin Koukousei-tachi wa Isekai demo Yoyuu de Ikinuku you desu!) a highschool student who is also the world's best journalist.
While still a high-school student, Mikogami Tsukasa (Choujin Koukousei-tachi wa Isekai demo Yoyuu de Ikinuku you desu!) is a genius politician who served as the Prime Minister.
Layfon W. Alseif (Chrome Shelled Regios) is a natural-born prodigy among even the Twelve Heavens Blade, being capable of becoming one at the age of ten. It was stated by even his master Lintence that he could break-down and master Kei Techniques after just seeing them performed once.
Frieza (Dragon Ball series) is a natural prodigy, having been born so powerful that he never had to train a day in his life...
...and when he did decide to train, he gained power comparable to gods within four months.
Rebecca (Dragonar Academy) is the second youngest Breeder to become a Dragonar.
Edward Elric (Fullmetal Alchemist), an alchemical prodigy, became a State Alchemist at age twelve.
Mukuro, later Nobume Imai (Gintama) is a masterful assassin even as a child, her skills earned her the position as one of the Three Wings of Naraku, and often called the "Bastard Child of the Death God".
In addition to his magical aptitude, Negi Springfield's (Mahou Sensei Negima) intelligence is such that he became a homeroom teacher for high school girls at age 10.
Medaka Kurokami (Medaka Box) is a natural genius, progressing through infancy at an accelerated rate and able to surpass even adults in all fields before she was even two years old.
Indra Ōtsutsuki (Naruto) was considered to be a prodigy, which led him to accomplish everything without the need for companions.
Madara Uchiha (Naruto) has been known to be a genius even as a child, being one of the first among the Uchiha to awaken the Mangekyo Sharingan, along with his mastery in fighting.
Sasori (Naruto) was considered as a child prodigy in the art of puppetry, mostly due to his loneliness in lack of parental love motivating his obsession in emotionless puppets.
As a young child who wasn't old enough to be a ninja yet, Zabuza Momochi (Naruto) effortlessly slaughtered over 100 Acemedy students without hesitation or pause earning the moniker of a Demon at a young age.
Itachi Uchiha (Naruto) has been heralded as a genius since childhood, as at age 13 he was selected to be an ANBU captain.
Before leaving the Leaf Village, Sasuke Uchiha (Naruto) was hailed as a genius and was one of the most skilled fighters
of the village.
Himawari Uzumaki (Naruto) not only awakened her byakugan at a younger age then her mom and aunt, but also mastered use of the gentle fist on her very first try.
Tony Tony Chopper (One Piece) had become an outstanding doctor at the age of 15.
Even at the young age of 15, Kyros (One Piece) was already proficient in combat having fought an entire gang by himself and eventually becoming recognized as the strongest gladiator of Dressrossa colosseum at age 24.
Rob Lucci (One Piece) was a prodigy in the Rokushiki martial arts, he could slay 500 soldiers when he was only thirteen years old.
Monkey D. Luffy (One Piece) is the youngest of the Worst Generation, and one of the strongest pirates of all time. He became recognized as a Yonko at the age of 19.
Sabo (One Piece) is one of the most powerful fighters of the Revolutionary army and the youngest.
Minks (One Piece) are natural born warriors from birth.
Grount (One Piece) is prodigious marine soldier, his great fighting prowess allows him to become a Marine Captain at age 17.
Charlotte Katakuri (One Piece) is the second strongest member of the Big Mom Pirates, having never lost a single battle since the day he was born. Until he finally tasted defeat at the hands of Monkey D. Luffy.
Charlotte Linlin (One Piece) was born immensely powerful, able to overpower giants even at the age of 5.
Yukari Sendo (Rosario + Vampire) is smart enough to attend high school at age 11.
Erina Nakiri (Shokugeki No Soma) is a child prodigy able to speak at infant stage and gifted with unique ability called "Gods Tongue" making her genius in her academy.
Becaming the king of the Chouga tribe at a relatively young age, Yo Tan Wa (Kingdom) has done almost the impossible for somebody her age, having conquered over half the Mountain Tribes of Qin and earning the title of Da Shang Zhao.
Originally a servant and a slave, Shin (Kingdom) trained himself in swordsmanship alongside his fellow servant Hyou. In the course of his life he has defeat far more experience opponents even before becoming a 100-man commander at the age of 13.
Noted by the elders of the Shiyuu Clan to be the most talented practitioner of the Priestess Dance of her generation, Kyou Kai (Kingdom) is a dangerously fearsome master swordswoman.
Haku Rei of Chu (Kingdom) is the youngest member of the Ten Bows of China, the most skilled archers throughout the 7 states of China, holding the spot of 3rd despite being only 18 years old .
Due to him being sent to brutal battlefields from a very young age and mowing down countless masses of enemies, Earl Shi (Kingdom) at age of 15 had already killed over 500 opponents.
Kenshirō Kasumi (Fist of the Blue Sky) was already a full-fledged martial arts master by the age of 3 before becoming the 62nd successor to the Hokuto Shin Ken (Big Dipper God Fist).
Originally watching his brother train while he watched on, Toki (Fist of the North Star) demonstrate his fighting ability by brutally beating a hunter who had killed his pet dog. Realizing that Toki had learned to fight by merely watching his brother, Ryuken began training him as well.
As a child, Kenshiro (Fist of the North Star) watched his adoptive brothers train in the art of Hokuto Shin Ken (Big Dipper God Fist) and decided to join them in the fight to become the successor. Despite being younger and more naive than his older brothers, Kenshiro was a promising student who ultimately earned the title of successor.
Sharrkan Amun Ra (Magi The Labyrinth of Magic) was prodigy in swordsmanship, able to defeat multiple strong adult robbers when he was nine years old.