Hi! So I decided to check SimPE to see how much time Herb had left as his aging bar looked full, but it says he has 65535 days left? Is he immortal or should I just keep playing until he dies? Thanks

It's probably just integer overflow because the number is -1. For some reason SimPE shows 1 day less than they actually have left, so you've just caught it at a time when Herb has 0 days left but hasn't died yet.

Oh I see, thanks so much for the help

To add to this, just in case you encounter this:

There is a bug in the game where an elder's sim bar appears to be full, as is they were ready to die, but the game doesn't let them die; it's like they're stuck on their death day and they continue to live past the end of their lifespan, and they kinda appear to be immortal. The sims that have this bug show they have 65535 day left to live in SimPe, which is the same amount of days sims who are already dead show.

This is fixed by moving the sim out of the lot and back in.