"But, like a puddle that freezes, my time has frozen. Inside this square room, where there is no change in seasons. I was always alone...while repeatedly seeing the same scenes in my dream...while viewing the endless night...But, slowly, light was starting to shine into the night."
The user can negate the age of themselves and others/objects, thus causing a matter, atom, cellular stand-still and can no longer change and grow older or be changed younger, thus the targets are stuck at that age forever.
May need to do certain things (meditation) or consume certain substances (blood, tanna leafs) to stay un-aging.
Dracula (Bram Stoker's Dracula)
Live Action TV
Adam Monroe (Heroes)
Clan Tralesta (Star Trek: TNG)
Welsper (Ah! My Goddess)
Asuka Shikinami Langley (Rebuild of Evangelion)
Dark Zagi (Ultraman Nexus)
The Doctor (Hellsing)
Flame Hazes (Shakugan no Shana)
Gen/Zen Fudo (Aquarion Evol)
Kaworu Nagisa (Rebuild of Evangelion)
Lord Genome (Gurren Lagann)
Mari Makinami Illustrious (Rebuild of Evangelion)
Mavis Vermillion (Fairy Tail)
Quinella (Sword Art Online)
Rei Ayanami (Rebuild of Evangelion)
Shenron (Dragon Ball)
Phantom (Marchen Awakens Romance); via the Zombie Tattoo
Shinji Ikari (Rebuild of Evangelion)
Sugar (One Piece); via the Hobi Hobi no Mi
Trafalgar D. Water Law (One Piece); via the Ope Ope no Mi
Ichigo Morino (Onegai Teacher); via Standstill
Kei Kusanagi (Onegai Teacher); via Standstill
Tenzen Yakushiji (Basilisk)
Tosuka (Highschool DxD)
Merlin (Nanatsu no Taizai)
Zook (Martin Mystery)
Gumball Watterson (The Amazing World of Gumball)
Darwin Watterson (The Amazing World of Gumball)
Jack (Samurai Jack); via time travel
Nyx (Fire Emblem Fates)
Cosmic Forge (Rifts)
Vampires (World of Darkness)
Demons Blood (Dog Days)
Avalon, The Everdistant Utopia (Fate/Stay Night)
Elixir of Life (Harry Potter)
Kings Jewel (Hayate no Gotoku); via the Royal Power
Zombie Tattoo (Marchen Awakens Romance)
Cruxis Crystals (Tales of Symphonia)
Keromet (Sgt. Frog/Keroro Gunso)
Pure Gold (One Piece)
Tenzen Yakushiji (Basilisk) having his symbiote "eat" away wounds and the ravages of time, maintaining his youth for over 200 years.
Shen Long (Dragon Ball) can grant eternal youth to the wisher, as Lord Slug and King Piccolo wished for their youth to be restored.
Due to a curse she placed on herself, Nyx (Fire Emblem Fates) has completely negated her ability to age.
By repeatedly regenerating her telomeres, Tomiko Asahina (From the New World) has largely negated her aging, maintaining her youth for 267 years.
Adam Monroe (Heroes) has regenerated so many times that his cells now regenerate and die in equilibrium, negating his aging.
Trafalgar D. Water Law (One Piece) can use the Perennial Youth Operation of his Ope Ope no Mi to grant eternal youth to another person, though he must forfeit his life in return.
Sugar (One Piece) ate the Hobi Hobi no Mi, which ceases her aging, and anyone who she changes into toys will also cease to age so long as they remain as toys.
Mitsuhiko Ishibori is the alias of Dark Zagi (Ultraman Nexus) when in possession of Hajime Yamaoka. After 18 years of possession, the host was actually old enough to be a middle aged man but his skin didn't age thanks to Zagi.
In her eagerness to have all the knowledge in the world, Merlin (Nanatsu not Taizai) uses her magic to stop her own time.
As a result of the usage of an incomplete version of the Law magic, Mavis Vermilion (Fairy Tail) stopped her growth entirely, forcing her into permanent youth.
Phantom (Marchen Awakens Romance) won't age because his Zombie Tattoo curse has finished its progression on his body, granting him immortality.