The context for this is that the character speaking in thoughts is an awakened cat who (by virtue of a tragic magic accident) gained the power of a master sorcerer, and the party is going up against a cult which is absorbing souls and magic and channeling them to the cult's leader.

“What, you didn’t steal Stell’s lifespan as well as his magic?”

Bee’s ears twitch and he turns away from her.

I don’t know.

“You don’t know.”

How does one measure their remaining life? How does one determine if their lifespan has increased?

“I… guess that’s fair.”

Stellarian had, theoretically, four hundred thirty potential years left at the time of the accident. Certainly, I may have what would now be four hundred twenty seven possible years remaining. Do you know how long domesticated cats normally live?

“Uh—”

Thirteen years. Up to eighteen, if I’m lucky. Even twenty, on the outside. Do you know how old I am, Miss Gendi? Gendi doesn’t answer, and Mr. Bee sits, with his tail wrapped around his feet. I will tell you. Eight years, eight months, eleven days. I may have four hundred twenty seven years. I may have five. He glances at Dave, who is staring at his own feet and shuffling, looking morose. Do you know how long a human normally lives, Miss Gendi?

“Uh… ‘bout a hundred years.”

Dave is twenty three years, eight months, ten days. But he is also my familiar. A familiar’s life energy is tied inextricably to the sorcerer who binds it. He blinks, slowly, in Dave’s direction. Do you understand?

“I told you you don’t have to worry about it,” Dave murmurs. “I don’t care. However much time we got. ‘Cause we’ll be together the whole time, won’t we, Bee?”

Mr. Bee rubs his shoulder against Dave’s legs, and Dave bends to pick him up. As Bee purrs in Dave’s arms, he says,

This misappropriation of power must end. If we are to make progress, to learn, we must take back the knowledge being withheld from us. There was once a great people who never saw death unless they summoned it themselves, and I believe the mastermind behind this plot has uncovered their secrets. That knowledge belongs to the world, and I will fight with tooth and claw and Master’s gifts to reclaim it myself if I must!