LONDON, Jan. 20 (Xinhua) -- Puberty now starts at 10 and lasts until 24, suggested a group of scientists studying adolescent health.

Writing in the Lancet Child and Adolescent Health journal, doctors from the Royal Victoria Hospital in Melbourne suggested broader adolescent years due to biological and societal changes in youths.

According to the research, earlier puberty has accelerated the onset of adolescence in nearly all populations.

For example, in industrialized countries such as Britain, the average age for a girl's first menstruation has dropped by four years in the past 150 years, according to a BBC news report.

At the other end of the spectrum, reaching the age of 19, in effect, does not mark the end of one's adolescent years.

"Although many adult legal privileges start at age 18 years, the adoption of adult roles and responsibilities generally occurs later," said the Lancet opinion piece.

The authors said delayed completion of education, marriage, and parenthood all contribute to shifting popular perception of when adulthood begins.

Also underpinning the theory are biological reasons: Brain continues to change and mature until a person reaches their mid-20s or even later, according to the article.

Thus, the research calls for an expanded and more inclusive definition of adolescence, which, according to the authors, is essential for developmentally appropriate framing of laws, social policies, and service systems.