Can zombies be killed dead by other "normal" means such as fire, electrocution, drowning, flies, satellite, disease, fright, cowplant, or scissors? I assume that zombies are immune to death by hunger or old age.
I'm not sure if zombies age or not, but I'm pretty sure they can die by any other means that would kill a normal sim. I know the short time I had a zombie living with a sim (Goopy, who's now a zombie townie), he had to eat.
Zombies don't age, only if you have a hack, mod, or cheat