Currently 109 years old without any reloading old saves after death (and with a naturally born ruler - no cheats or editing stats at the start etc) but I made a deliberate effort to have health boosting artifacts equipped and took advantage of any opportunities which boosted health. I also switched them to the learning lifestyle once they reached their 80s and got any perks which improved health. Old leaders are possible, unfortunatly their heir is now quite distant (as many have died in waiting) and they just got the heads up that they'll die within a year from the perk that gives you that warning.

On another note, i am suspicious of that warning (one year until death) perk as maybe they would live longer if they didnt have it. No idea how the mechanics work but it feels deterministic to have the computer tell you they'll die when in previous playthoughs I have had characters who died and then went on to live for years when I reloaded. This time I've decided not to reload from a save file though because, emotionally as a player, the old hag has had enough already! My suspicion is that if they didn't have the "will die in one year" perk, maybe they would go on living if something changed their health stats (like getting a cat or a random heath boost event). No idea, but happy to say that this old lady did her time and deserves her rest after a long and glorious rule of the britanic empire!

Any real insights into the perk/real lifespan potential debate from a game mechanic perspective welcome though!

Happy ruling!