Saguaro Cactus takes about 75-100 years to form it's first arm... although some never grow arms. These arms generally bend upward and can number over 25. Saguaros are covered with protective spines, white flowers in late spring, and red fruit in summer. It is estimated that saguaros can live to be as much as 150-200 years old. Saguaro are very slow growing cactus. A 10 year old plant might only be 1.5 inches tall. Saguaro can grow to be between 40-60 feet tall.