The ability to accelerate or reverse the age of one's body to the point where they are at their strongest. Variation of Super Form.
The user can either accelerate or reverse the aging process of themselves placing them to the point where they are at their prime. Their supernatural powers and physical condition are drastically increased as well as eliminating the negative effects of age. Some users may gain new abilities if they age to their older self rather than those who regress to their younger self.
Lambo (Katekyo Hitman Reborn); via 10 year Bazooka
Libra Dohko (Saint Seiya)
Mosquito (Soul Eater)
Neliel Tu Olderschvank (Bleach)
Zangetsu/Tensa Zangetsu (Bleach); via Bankai
Gon Freecss (Hunter × Hunter)
Tamamo No Mae (Omamori Himari)
Nightin (One Piece)
Touhou Fuhai (Rosario + Vampire)
Walter C. Dornez (Hellsing)
Time Master (Freedom Force)
Silva (Jibaku-kun: Twelve World Story)
Princess Valkyrie (UFO Ultramaiden Valkyrie)
Demon God Crystal (Dog Days)
Hero Crystal (Dog Days)
Spirit Crystal (Dog Days)
After being turned into a child by Ultimate Shenron, Goku (Dragon Ball GT) is able to return to his adult form whenever he becomes a Super Saiyan 4, allowing him to once again use all of his abilities, like Instant Transmission, to their full potential.
After her Third Origin was awakened, Sherria Blendi (Fairy Tail) was able to utilize her full future potential power as well accelerating her age to adulthood in exchange for never being able to use magic again.
After being consumed with extreme rage, Gon Freecss (Hunter × Hunter) assumed an adult form, enhancing all of his abilities.
While he normally remains in the form of an old man to preserve his strength, Touhou Fuhai (Rosario + Vampire) is able to return to his younger self to release his true power.