Most parents had noted the onset of symptoms by age
16 years, which is slightly lower than the age found by
Perlis et al. (2004) in the Systematic Treatment Enhancement
Program for Bipolar Disorder. That study found a
mean age at onset of 17.37 years (SD 8.67), and identified
27.7% with an onset less than 13 years, and 37.6%
between the ages of 13 and 18 years. Approximately 60%
of that cohort had onset prior to 18 years. The research
indicates that the onset of bipolar disorder occurs primarily
over the adolescent years with the mean age at onset of
bipolar disorder ranging from 17.4 years to 23.3 years
(Kupfer et al. 2002, Grant et al. 2005, Goodwin &
Jamison 2007, pp. 155–220). This is the case across studies
that have included bipolar I disorder only, bipolar I and
bipolar II disorders, and those with bipolar spectrum disorders.
Peak age at onset identified is in the 15–19 years age
group with 53–60% of those with bipolar disorder having
onset prior to 19 years. Given its onset during a crucial
period of personal and social development, Inder et al.
(2008) have noted its effect on identity development
because of difficulties in establishing continuity in their
sense of self.