10 years seems like a long time to grow an arm. But did you know that the 1st 10 years of life for a saguaro might get it just 1in of full body growth? By 70, yes 70 years old they can be 6ft 6in. That’s as tall as Michael Jordan. By 70 is when they first begin to flower. When they turn 95 it’ll be around 14ft high and can begin to grow its first arm.