The life of a saguaro isn't easy. According to the park handout, a seedling grows only a quarter-inch the first year, takes up to 15 years to reach one foot, 100 years to reach 25 feet and 150 years to reach 50 feet. By the time it starts to grow its first arm at age 75, an entire human lifetime has passed. The saguaros get less than 12 inches of rain in a typical year, suffer through months of drought, are struck by lightening, battered by wind, frozen in winter (which biologists believe is the greatest cause of saguaro deaths at this their northernmost range), baked by 100 F daytime summer temperatures, crowded by urban development (which affects the water table and runoff patterns), and are pitted against wildlife that eat the seeds and seedlings and bore holes in the trunks and arms for nests. It doesn't flower until it is about 30 years old and then each flower opens only for a few hours at night from April through June.
Despite these challenges, with park protection the saguaros appear to be doing well. If you ever get to Tucson. . . .