Cornell University reports that early onset of self-injury usually occurs around the age of seven! The group of early adolescents between the ages of twelve and fifteen is where self-injury more commonly begins to be seen but the age of seventeen has been found to be the most frequently self-reported age for the first act of self-injury. Later onset spanning twenty year olds is also seen but less frequently.
Since self-injury is such a private affair and often kept secret it is hard to determine the frequency at which it is engaged. Statistics rely solely upon self-reported behaviors which often lack objective and subjective validity considering the emotional struggles of those masking or expressing through SI. Depending on the stressors and the strength and frequency of SI inducing triggers that are encountered, harming oneself could range from multiple times a day to occasional once a month releases.
The most common duration of self-harming has been found to be around five years. Acts of self-injury are more cyclic than linear. Periods of frequent use of SI followed by weeks or months of abandonment… only to resume it again is normal. Although it can last well into adulthood, this would be the exception and not the norm.