This is an elderly-aged version of Timmy that appears only in "Timmy's Secret Wish", where he interacts with several other aged up characters before Cosmo and Wanda eventually reunite with him and restore him to his normal age.
Due to the way this wish was brought on Timmy by punishment, it seemed to temporarily have erased the normal timeline where Timmy grows up, marries Tootie and has twochildren. Instead, Timmy is still living in his parents house, and everyone in the world is aged along with him fifty years into the future with no other births or deaths, making the youngest person in the world 50 years old and previously adult or elderly characters like Mr. Crocker's Mother impossibly old.
In the television movie "Timmy's Secret Wish", Timmy Turner, along with the rest of Dimmsdale, is aged fifty years quickly by Father Time at the orders of the Fairy Council. This was because they had learned Timmy had wished secretly to stay ten years old fifty years ago. Despite their intent to correct things, the Council's actions actually had disastrous effects on Dimmsdale, as technology was also progressed fifty years, and everyone was too old, ignorant, and infirm to use it correctly. Timmy seemed to vaguely recall his fairies, and after meeting with Denzel Crocker (the only person visibly unaffected by the aging, due to previous trauma), he joined forces with him and used a portal to Fairy World to reunite with them and save Poof, who had been erased from existence and sent to the Hocus Poconos due to Timmy losing his fairies (Poof was originally wished for by Timmy). Cosmo and Wanda also restored Timmy to his normal ten year old age. After sacrificing himself to save his fairies and Poof, Timmy is stranded behind in the Hocus Poconos, but ultimately brought back to Fairy World by the Council, who reward him his fairies back and reverse the effects of the aging wish on everyone else.