Any thing useful to use 5 gallons of old peanut oil?

Fry some turkeys.

As long as the top was on tight it should be good for years. The biggest benefit of peanut oil is it doesn't go rancid like vegetable oils.

I've used the same oil for dozens of turkeys for over two or three years. I would just filter it after each use.

Cook something with it.

If you're hell bent on getting rid of it, use it to start fires.

Cholesterol make get me before that with all them turkeys.

I know it kills grass

If not open should be good for years.

Biodiesel or contact your local swingers club