If well maintained,a good quality top-grain leather should last 20 to 30 years. The biggest enemy of long life for your leather furniture and car interiors is sun damage.
The effect of sun damage varies depending on the grade of your leather. Full aniline leather(unfinished, natural) is most susceptible to fading. It can fade from dark to almost white in color if exposed to direct or indirect sunlight. Sun can also cause the leather to lose moisture, creating a rough, dry surface. Semi-aniline leather (finished surface) is not as susceptible to fading, but sun damage can result in cracking and peeling of the surface and, in extreme cases, the leather can shrink and pull away from the seams.
Thankfully, most of the damage on both types of leather are repairable. The cost of repair varies depending on the severity of the fading, cracking, or peeling. If the leather has shrunken to the point of pulling away from the seam, it is usually not repairable. (We see this a lot in convertible automobiles.) In this case, replacement of leather is your only option.
The bottom line: keep your leather furniture away from any windows with direct sunlight. With both furniture and auto interiors, UV tinting on windows is a good option to help protect your investment.