As long as it's not green. Potatoes have been eaten raw by many a hungry person. If your thinking it's going to taste like a cooked potato you will be mistaken it is like any other raw tuber. Raw...
Anytime, but like a banana, it will taste better when it is ripe and it won't give you a tummy ache. Have you tried them deep fried? Wow! Freeze the plantain first, then slice it and drop the frozen...