Plant and animal cell replacement question

Hello, I have been trying to get the answer to the following question,
with no luck:

Is it the case that all plants and animals, including humans, turn
over every single one of their cells during the course of their mature
life? One hears stories to the effect that human cells change in their
totality every 7 years, or (on the contrary) that certain neurons do
in fact remain in the human being until the person's death, etc. But
I've never seen an authoritative statement of the facts.

Can anyone help?

Thanks,
D. Oderberg
UK