It should be stamped or etched on the lower part of the bottle in tiny numerals. This is often difficult to see, or impossible if the bottle got skipped. The last four digits are 24-hr time of whatever date the stamp is. It should begin with an L, then letters or numerals designating distillery of origin, then three numerals designating day of the year. Somewhere in there the year is coded by various means. On wine bottles, I have seen, for example, LC12314091533, which would be May 3, 2014, line 9, at 3:33 p.m. There is some variance with products or companies or origins. Can you find the number, and if so, what is it?
Addendum: Or not. On reflection, the bottle code thing of which I speak is fairly recent, so I guess that's out for an older bottle. Good luck. Spirits, by the way, don't "age" in a good way after bottling.