They live as long as you feed them and have a paper towel and spray water on them so they can drink.
A mealworm can live up to one year.
A mealworm itself (larva) can live for 10 days before molting into a pupa.
I read that they live for about 5-10 days, but I have had mine for a month now.I put the bedding in a separate container and had lots of meal worms. but the adults haven't died yet. Mine has lived...
4cm or a adult is about 1 inch.