It's shochu, not sake. This one is made from barley.
Here's the product page. 吉四六 | 二階堂酒造
The sticker just says not for consumption of minors and to be careful when opening. I'm not sure what the 8,5 means. It could mean mid-1996 because 1996 was Heisei year 8.
What is the average shelf life of shochu? Technically shochu does not have a shelf life since distilled alcoholic beverages are not so high in sugar and/or protein content. Shochu is usually more than 25% in alcohol content, so technically it can be enjoyed for a long time without risk of decomposition. Many times people age shochu more, just as whiskey enthusiasts prefer well-aged bottles.
Shochu should be kept in a cool, dark place. Once it is opened, the taste of the shochu begins to change progressively as time passes. Once opened, shochu should be consumed within a couple of months.