Idiopathic guttate hypomelanosis occur at age of 20years?

Rarely: This condition is usually seen in individuals a bit older.

Possibly ,unlikely: Idiopathic guttate hypomelanosis, an acquired, benign leukoderma of unknown cause. Most commonly in middle-aged, light-skinned women, but increasingly seen in both sexes and older dark-skinned people with history of long-term sun exposure. It is a benign condition. The cause is not known, but it appears related to the effect of sun on melanocytes.