I don't know what is meant by "service life" but as far as 25 years.... here is a reference regarding the 100 series.
"Excerpts from article in Automotive Industries, Feb. 1998, by Lindsay Brook
Design/Engineering: Chassis
Design of UZJ100, as the '98 Cruiser program is coded, was frozen in mid-1994, says veteran chief engineer Takeo Kondo. At that point, the previous FJ80 model was three years old. And as on every previous Cruiser, UZJ100 has body-on-frame construction.
"There was never any consideration of unibody design," Kondo tells AI. "Long-term durability has always been the number one goal of the Land Cruiser program," he explains, "and we expect these vehicles to be on the road for at least 25 years." Range Rover was the program's primary benchmark, particularly for suspension articulation, chassis stiffness and interior appointments."