Bourbon and other hard spirits age in the barrel, not in the bottle. They become lower in proof while doing so. You are freely permitted to dis-concur with me, but I suggest you look it up first, because, what I am saying is true. Liquors get "smoother" as they age. Once in the bottle, the aging is mostly limited to the amount of air in the bottle and thus pretty much stops. I like smoked meats, smoked fruits, smoked wines etc., and I am eager to try the devil's share. Sounds very attractive to me, but then again, who likes eating or drinking portions of smoked wood? I must have been born with a hard head.
the question isn't whether the liquor ages in the bottle (it does, but generally not enough to notice.) the question is when do you have to throw it away. I collect bourbon, and obviously being a cook, I like to drink. A few days ago I turned 24, I had a few friends over and I gifted each one with a pour from a bottle I received on my 18th birthday. It still tasted exactly as it did when I opened it 6 years ago. The bottle was about 1/3 full, none of us got the runs, none of us got sick.