The thing is we've had lots of advances in the fight against aging. We've discovered stuff like metformin, akg, melatonin, nad+ boosters, sirtuin activators. We've even discovered that some of the yamanaka factors can be used to rejuvenate the epigenome all the way if needed.

Right now preliminary studies in rodents seem to show promise for astaxanthin too.

If you go by Aubrey De Grey's notions of aging, it would be extremely difficult for a monkey to double lifespan or for a human to double lifespan. Yet we've seen that it is likely our common ancestor with monkeys had monkey like lifespan, and a few minor tweaks tripled lifespan in humans. The changes were easy not uber herculean engineering feats as Aubrey supposes. Analysis of the genomes of even longer lived mammals like Bowhead whales show lack of many of the engineering suggestions of SENS in their genome.

Again the longer lived a species is, the fewer mutations or changes are likely needed to make it an ageless, or biologically immortal species. Humans are pretty long lived already. An intervention that doubles or triples lifespan in a shorter lived organism, might actually make humans ageless or biologically immortal. This might only need be a cocktail of a few drugs and nutraceuticals.