Men grow extremely fast between the ages of 11-15, and during this growth spurt the increase in height can be as much as 12 inches (30cm). After the age of 16 the increase in height is more gradual and boys usually stop growing between the ages of 17-20. So the majority of guys will reach their final height and stop growing when they are around 20 years old. During this growth phase, feet, hands, legs, and muscles start to grow. A man’s shoulders will also broaden and boys start to grow hair on their hands, legs, armpits, and chest.