Scientists have changed their idea of adolescence - the period when children develop into adults. It used to be around our teenage years, but now scientists say it can be between the ages of 10 and 24. Puberty once started around the age of 14, but better health means it can start four years earlier, especially in the developed world. Adolescence now ends later because we stay in education longer, and delay things like marriage, parenthood and working.
The scientists published their study in a journal. They say society needs new laws for adolescents. A researcher said: "The adoption of adult roles and responsibilities generally occurs later." They suggested extending youth support services. This could be a problem because there is a big difference in the legal age at which nations recognize adulthood. In Indonesia and Yemen it is 15, but in Singapore and Zambia, the age is 21.