"Manufacturers like Elf and Valvoline state that as long as their oil was stored under optimal conditions, unopened containers should be good for a practically unlimited time. However Mobil1 says that their oil has a shelf life of five years." 17 Mar 2016
I usually have a stock of oil on the shelf and wouldn't be at all concerned about using 5 year old oil, be it synthetic or mineral. Which is just as well because the vast majority of oils marketed as fully synthetic aren't. Even Mobil 1 isn't fully synthetic these days. And the price that MB's own oil is selling for means that definitely isn't fully synthetic either.