Others families live into their hundreds without any effort. It would seem the first thing to do is to figure out a way to fix DNA.
In 1986 exercise physiologist Kenneth Cooper published an inventory of the risk factors that might have contributed to Fixx's death.[6] Granted access to his medical records and autopsy, and after interviewing his friends and family, Cooper concluded that Fixx was genetically predisposed—his father died of a heart attack at 43 after a previous one at 35,[7] and Fixx himself had a congenitally enlarged heart—and had an unhealthy life: Fixx was a heavy smoker before beginning running at age 36, had a stressful occupation, had undergone a second divorce, and gained weight up to 214 pounds (97 kg).[8] Medical opinion continues to uphold the link between moderate exercise and longevity.[9]
Your pill would need to do a lot of heavy lifting. I'm no doctor, but your pill would need to deal with mental issues (dementia of all kinds etc) and physical issues, like muscle mass, bone density, flexibility, skin elasticity and lots more.
There are very few, dare I say no, 90 year old that could pass for 70 - what sort of condition would 120 bring? Or 130 etc?
As an expert in one field, used to customers waving their hands telling me "this won't take long for you to do, it's very simple", I feel like your belief in (medical) technology, and what is possible, may be just a touch optimistic.
There are already large mammals - bowhead whales - that can live 200 years. Perhaps we can adopt some of their longevity traits without having to become giant ocean creatures.
The frailty comes from somewhere, like depletion of certain stem cells that produce new tissue.
Technology hasn't really taken us past mid 80s. It seems plausible that it could, but that's based purely on speculation, so it could be false.