The lifespan is like this in my Bowie family:
David Bowie becomes an Elder in 5 days, Bowie Stardust(their cat) is already an elder, the cat's been old for 3-5 game days max...Lifespan is on Normal, so David Bowie will die of Old Age 10 days after becoming Elderly, Bowie Stardust...I'll be shocked if he dies when I load the family today.
His wife, Destiny Bowie, Freddie Mercury, Thomas Jerome Newton and Ziggy Stardust all have the Immortal CC trait, so none of them will die or age, I prepared for their cat's death by adoping a female cocker spaniel puppy I named Brandy Bowie, for the cat, I wanted Bowie to die in peace, so I disabled Witnessing Death for their cat using MC Command Center, but I'll reset Witnessing Death to Enabled once David Bowie gets old, as he'll most likely want his wife by his side.
More to the point, seeing my cat die in the game will devastate me, as I live with two 15 year old cats irl, one is deaf, his name is Digit, his brother is named Ezra(I nicknamed Ezra "Bowie Z," though), we're all saying Digit will go first because he's already lost his hearing...Our Youngest cat, Sammy, is only 3 years old, so he has a long way to go before he gets old.
Whenever my Sims/Pets get old, my game likes to jumpscare me into thinking that they're dying, why is the game such a jerk to me?!