Time
Time's credentials in the longevity department are, one might say, unimpeachable. It has existed since existence itself began, predating matter, energy, and certainly any being capable of measuring it. Physicists estimate the universe at 13.8 billion years old, and Time has been present for every single moment of that incomprehensible span. Moreover, Time shows no signs of fatigue, no indication of retirement, no hint that it might one day simply stop bothering. It shall persist until the last proton decays and likely beyond, into whatever unknowable state follows our universe's eventual heat death.
The remarkable aspect of Time's longevity is its unchanging consistency. Unlike physical entities that degrade, corrode, or simply give up, Time maintains its relentless forward march with machine-like precision. It is, in essence, the very measurement by which longevity itself is calculated.
Yoda
Yoda's 900 years of existence represent an achievement remarkable by any biological standard. Few sentient beings in the known galaxy have matched such a lifespan whilst remaining mentally acute and physically capable of dramatic lightsaber combat. His longevity has allowed him to train Jedi across countless generations, accumulating wisdom that spans the rise and fall of multiple galactic governments.
Yet one must acknowledge the fundamental limitation here. Nine hundred years, whilst impressive at dinner parties, represents a mere 0.0000065 percent of the universe's age. Yoda's centuries of meditation, teaching, and curious grammar constitute but a brief flicker against Time's eternal backdrop. He has, despite his considerable years, merely borrowed a tiny fraction of Time's infinite domain.