I most whole-heartedly agree with Asa and Jim-NE that good lures will last many years. And some (like Doc says) age well like a fine wine.
However, I had a bad experience with old urine. It may have gotten contaminated some way, not sure. The urine was stuck back and forgotten about for about 3 years. Normally, I would use the "left-overs" the next season and start on fresh. But somehow, this had gotten misplaced and was in the 4th year of me having it. I know it was good when I put it away after that first season, since it did it's job very well. It was not a home collected urine but that from a very reputable supplier.
Anyway, when I went ahead and tried it in that 4th season, it was a disaster. Everything shyed away from my sets where I had used it. After a couple of rains, I re-set the exact same locations with new urine and made my catches as expected. Sorry guys, but I just don't trust urine that is several years old after that one. How much time did I waste making those sets and using the bad when a gallon of good would have netted me much more $$$ than empty traps did.