This is the limit.
Although there are no "Martial Arts Scriptures" circulating in this world, after Condensing Spirit and Unifying Dao, the lifespan of Four-Realm Warriors generally reaches 150 years. If one avoids conflicts and does not sustain any hidden injuries, one could even live up to 200 years.
If one were to cultivate the Longevity Jue, which focuses on nurturing health and extending life...
There is no data on this at present, but Xu Yang estimates that there should be hope to live to 300 years, or at least 250 years at the very least.
That is to say, apart from the three Grandmasters, the four Holy Monks, the Evil King of Heavenly Blade, and other illustrious figures known to the world, there might be many old undying masters hidden in the shadows, past grandmasters.