London, Jan 20 (IANS): Gradual changes in biological growth and social role transitions -- coupled with delayed marriage and parenthood -- have pushed back the period of adolescence between ages 10-24 rather than the previously known 10-19 years, a Lancet study said on Friday.

The past century has seen drastic changes in the definition of adolescence, which encompasses elements of biological growth and major social role transitions.

"Rather than age 10-19 years, a definition of 10-24 years corresponds more closely to adolescent growth and popular understandings of this life phase and would facilitate extended investments across a broader range of settings," said study lead author Susan M Sawyer from the Centre for Adolescent Health at the Royal Children's Hospital in Melbourne.

The study, published in the journal Lancet Child & Adolescent Health, revealed that an early puberty has accelerated the onset of adolescence in nearly all populations, while understanding of continued growth has lifted its endpoint age well into the 20s.

As a result of lifestyle changes, genetics and environmental factors, early puberty for girls at age 8-10 is the new "normal".

While menstruation is a natural process, an early puberty results in various health issues, like depression and behavioural issues as well as the risk of cardiovascular disease and some cancers.

Similarly, young adults continuing their education for longer period, delayed marriage and parenthood, has pushed back popular perceptions of when adulthood begins.

"The transition period from childhood to adulthood now occupies a greater portion of the life course than ever before at a time when unprecedented social forces, including marketing and digital media, are affecting health and well-being across these years," Sawyer noted.

An expanded and more inclusive definition of adolescence is essential for developmentally appropriate framing of laws, social policies and service systems, the researchers added.