Puberty announces itself to girls with growing breasts and their first period. This process, fuelled by significant hormonal changes, is hard on girls no matter how mentally mature they may appear.
In 1901, the median age for girls going through puberty was approximately 14 years and there was little difference among ethnicities.
But things have changed. As Professor George Patton, of Murdoch Children's Hospital, said recently: "In the course of the 130 years, between 1830 and 1960, we saw a drop in the age of onset of periods from about 17 years down to about 12-and-a-half, 13 years."
Several factors have led to the earlier age of puberty. Most scientists agree that improved nutrition plays an important factor, as does the ability for children to develop with a degree of emotional, social and financial comfort.
However, with rates of puberty starting an additional two to four years earlier scientists are still trying to determine the cause. Danish research shows puberty is occurring even earlier, with many girls showing signs at just 10.
It has been argued that excess fat can affect oestrogen, so the researchers examined the relationship between age of puberty and obesity. They found that children aged seven with weight issues were more likely to enter puberty earlier. However, they also noted there was a universal trend towards premature puberty that could not be explained by obesity alone.
Additionally, different ethnicities are now beginning to experience different pubertal rates, which may suggest social and economic inequality has a physical impact. This is a particular concern with for African-Americans, nearly 50 per cent of whom display signs of puberty at the age of eight.
Environment is also considered a possible factor, with the presence of hormones, chemicals and pollutants showing an impact on the development of fish and animals. Professor Paton has said that this exposure to endocrine-disrupting chemicals is "one of the things people are speculating on".
Patton and his colleagues have been studying puberty and how it is changing in Australian children using the Longitudinal Study of Australian Children.
One thing the team have discovered is a connection between childhood mental illness and early puberty. While many professionals believe early puberty can place mentally unprepared children under extreme stress, they are only just becoming aware that stress can also be a trigger for early puberty.
According to their research, Australian children who reach puberty early show problems with "emotional and social adjustment" from the age of four on. There is a suggestion this may be associated with disruption in the home or broader community.
"What we found was that as early as the age of four these kids differ in their social and emotional profiles," Professor Paton told ABC Radio's AM program. "So they're having more difficulties at the age of four with anxiety, with unhappiness, with getting tense and not knowing what to do about it. They're having more difficulties with their peers, finding friends, with bullying, being included, as early as the age of four."
Patton and fellow researcher Fiona Mensah believe "early puberty may be part of an accelerated transition to adult development which begins early in life. This, in turn, heightens the risks for emotional and behavioural problems". So, while trying to recuperate from stress and hampered development as small children, the early onset of puberty complicates matters as unprepared children try to get used to physical change.
Research into our falling rates of puberty is ongoing and further examination is required to try to uncover the mystery and factors in play for this biological development. This recent research, however, reinforces the importance of providing safe, supportive and healthy environments for children no matter their age.