There is no single useful lifespan number for every door
A garage door is a system made of sections, springs, rollers, cables, tracks, hinges, seals, and an opener. Those parts age at different rates. Usage cycles, climate exposure, maintenance, material, installation quality, and accidental damage all affect service life.
Replace only what the condition justifies
A worn spring or opener does not automatically mean the door sections are finished. Likewise, badly damaged sections can justify replacement even when some hardware still works. Use repair vs. replacement to evaluate the whole system.