Included were: (i) original birth cohort or cross-sectional studies retrospectively assessing age at disorder onset, or prospective incidence studies [30], (ii) focusing on the general population, (iii) assessing age at onset of mental disorders, defined according to international classification diseases (ICD) or diagnostic and statistical manual (DSM)-any version criteria, or by established psychometric instruments with validated cut-offs that defined ICD/DSM diagnostic categories, (iv) written in English.
