You probably didn't explain death properly to him. Old age isn't the only cause of death.

See this is the reason I want kids

He's not wrong...

Please let me adopt that child

Um why are you talking to your toddler about death?! wtf???

well. you better hope that your son does not keep this memory later on in life, but please OP, think about if its appropriate to tell him those things

People are wondering if a kid can grasp the concept of death. Yes they can at that age. I had a pet Hamster at around 3-4. He was white and I named him snowball. Well I took snowball out of his cage to play and he bit me. It hurt so I wanted to punish him. I found him, picked him up, put him in the cd player and slammed the lid down on him. It crushed his neck and he died. I knew he was dead, I wasn't meaning to kill him just punish him but he died. That was my first experience with death. I hid his body because I didn't want my mom to find out. I later confessed because I felt guilty for killing him. The world isn't a bunch of rainbows and butterflies. Things die and there is no correct age to learn about it. Things die when they die whether the child is 3 or 30. Stop sheltering kids and maybe they'd be smarter. This is why we have kids having kids since there are those who think you can't get pregnant standing up. Their parents probably avoided the topic since it was awkward. Would you rather your kid kill an animal and not understanding what death is and that it won't come back or have a kid talking about death?

Try explaining the meaning in a much further or easier way so he might understand what you meant (:

tell them it is not appropriate to say things like that

Sounds like he sees dead people.