How tall are 15-year-old saguaro cactus plants?

Common opinion is that a saguaro grows about an inch to an inch and a half a year, give or take depending on the weather. But there is tremendous variation between individual specimens. One saguaro that is 150 years old might be roughly 150" tall, or about 12 feet while another in a more sunny position or with access to more water might reach 40 feet.