Three hundred years old

There is a guy who arrives to a town in western Spain, he seems like a charlatan and begins to advertise a potion, which supposedly keeps him young despite the fact that he is three hundred years old.
A farmer, having doubts, approaches one of his assistants.
“Hey, is it really true that this guy has lived three hundred years?”
“I don’t know, I have only worked with him for two hundred.”

Worry about warnings