When does puberty happen? Puberty usually begins at around the age of 11 for girls and 12 for boys. Exactly when puberty starts varies from one person to another. Anything between the ages of 9 and 14 is perfectly normal. Occasionally, puberty can start earlier than 8 or be delayed until after 14. If this happens, a doctor may recommend a course of treatment to adjust the timing of puberty. If you're a girl, it's sensible to speak to your school nurse if your breasts start to develop before you are 9 years old, or if they haven't started to develop by the age of 14. If you're a boy, it would be sensible to visit your doctor if your genitalia (testicles and penis) or pubic hair grow before you are 9 years old, or if they haven't started to grow by the age of 14.