If we're talking about unused oil sitting on a shelf, then no, there is no shelf life. You could use oil refined even 50 years ago, though it won't contain the same additives as newer oil. However, you shouldn't leave oil in your tank for more than a year without use, it could solidify and become gelatinous.
Yes,all petrolium products have a shelf life. Oil, depending on manufacture and product normally ranges from 1-2 years,oxidation being the main reason it goes bad so change it out
IT probably does but its not going to be significant. Oil isn't as reactive as say gasoline which can go bad after the years. Oil on the other hand should stay good for many many years. On the other hand it is super cheap so why risk it anyways.
As long as it is unopened, it should have a shelf life of 8-10 years. Be sure to shake it up well to insure all components that may have separated are blended again. If previously opened, replace with a new bottle.