How much children grow in a year is related to whether they reach puberty and their gender. Both boys and girls grow an average of 25cm from birth to 1 week of age, 12-15cm per year from 1-2 weeks of age, 12cm per year from 2-4 weeks of age, and 7-8cm per year from 4 weeks of age until they reach puberty. girls grow at a decreasing rate of 7cm, 6cm, and 5cm per year from the age of 11 years of bone age until they stop growing at 18 years of age. Boys start at 13 or 13 1/2 years of age and grow at a decreasing rate of 7cm, 6cm, and 5cm per year until they stop growing in height at 18 years of age. The average lifetime height of our girls is 160.6cm and the average lifetime height of boys is 172.7cm.