Well in the Doom Patrol series, the only thing stopping Niles from Aging was the Talisman which he eventually gives up after which he ages and dies.
Now further explaining Rita Farr, The gas that Caulder exposed Rita to altered her cellular structure and allowed her to stretch her body but also to completely collapse it into a blob form. This rearranging of her cells allows her to restructure her body subconsciously, averting the aging process.
Next, Larry Trainor, born in the late 1920s, was a pilot testing an X-15 as part of the Mercury space program for NASA when he was exposed to the Negative Spirit as part of a plot set up by Niles Caulder. Having left Larry on his own by the start of Doom Patrol season 3, the Negative Spirit inhabited Larry’s body for around seventy years before separating. While at one point Larry seemed to start to die if the Negative Spirit was absent for too long, after a trip to the Negative Space he can now survive without it. Larry’s extended lifespan is thanks to the radiation that he was exposed to from the Negative Spirit, which also left him disfigure
Cliff Steele - Born in 1956, race car driver Cliff Steele’s body was destroyed in a car accident when he was driving, yet another plan that had been put into motion by Niles Caulder. Cliff Steele’s (Brendan Fraser) brain was put into a robotic body, making him Robotman. His external shell does not age, beyond the occasional dent, and was able to be reassembled after it was shattered at the end of Doom Patrol season 2. While this was thought to make Cliff immortal, his brain, sustained by a nutrient tank, has started to age and in Doom Patrol season 3 he is thought to have developed Parkinson’s disease.
Kay Challis - Jane is one of the many superpowered alters that exist because Kay lives with dissociative identity disorder born of childhood abuse and trauma. Kay was born in 1950 and aged normally until she was experimented on in a mental institution under the directive of Niles Caulder in 1976. This gave each of her many alters different superpowers, and she has not aged since. While it is possible that one of the personalities has a specific longevity power, the idea that is most strongly supported by Doom Patrol is that the way that Kay shapeshifts between identities and appearances also helps to slow or reset the aging process, keeping her eternally at around 26 years old.
Cyborg - It is unclear how long Cyborg could stay alive for as his onboard computer, Grid, is designed to repair damage to his physical body and this could extend his life. The cybernetics fused to his body use nanotechnology to heal and repair him and they have stopped his aging process at 18, meaning that he has not grown or notably aged since then.
Dorothy Spinner - Dorothy is the daughter of Niles Caulder and Slava (Pisay Pao). Dorothy was born in the early 1900s and after Niles Caulder rescued her from the carnival she lived for the next 90 years on Danny the Street, shut away and never aging in all of that time Her mother, Slava, was a metahuman who possessed extreme longevity and had outlived several generations of her tribe. It is likely that this power passed to Dorothy. Additionally, when Dorothy leaves Danny the Street in Doom Patrol, she begins aging and starts to go through puberty, so it is likely that Dorothy herself had been in stasis for nine decades during her time on Danny, and now that she has stopped living on Danny permanently will age to physical maturity and then remain ageless going forward.
Eric Morden - Originally a member of The Brotherhood of Evil, Eric Morden was kicked out and went missing in South America in the 1940s. In 1949, Morden paid the Nazi scientist Heinrich Von Fuchs to give him superpowers. During the process, Niles Caulder destroyed Von Fuchs’ machine while Morden was inside, causing Morden’s body to suffer unexpected side effects. Becoming Mr. Nobody, Eric Morden became semi-non-corporeal and exists somewhat outside of time, as represented by his ability to break the fourth wall, serve as the narrator, and demonstrate a type of omniscience. Because of this, he does not age and it is unclear whether he could ever truly be killed within the Doom Patrol TV series continuity.
This article explains the reasons for the slow aging of the the rest of the members, and then the Sister of Dada, the information given in my answers are excerpts from the same article. They successfully explain how niles affected their aging process
