When do the girls who are over the age of puberty, but have not had their first period yet be accountable (mukallaf)?

Accountability for religious rules starts with puberty. Girls are considered to have reached puberty, when they start to menstruate.

A girl who has not reached puberty until the age of 15 is considered legally to have reached puberty and accountable as of the date when she completes the age of 15 (Mawsili, al-Ikhtiyar, II, 234-235; Tahtawi, Hashiyah, 108; Ibn Abidin, Radd al-Muhtar, IX, 226).

Source: Presidency Of Religious Affairs The Turkey, High Board of Religious Affairs FATWAS

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