Most of them last a good 10 years or more. there a couple things that directly effect the life of an electrolytic capacitor. Temprature, is the most detrimental to a capacitor. Excess heat may shorten their life to less than 10 years if is hot enough. Computer grade capacitors are rated to 85 degree C, where industrial grade are rated much higher at 105 degree C. We have seen units come through here over 15 years old running on original capacitors, some still test good. However as part of our refurbish process these are generally the first thing to go.
Oh yah sorry Marie, that would be the voltage rating. Derating the voltage can help them last longer too. In other words, if you can use a 35 volt rated cap in place of a 25 volt it should help life span a little. None as much as the heat though ok?
So keep your caps cool.