The modern study of Ibn Mujahid's selection of the seven readers works from his writing and its later citation; it does not supply his own birth or death year, and no other catalogued source does either.
What would resolve this A biographical dictionary entry from the classical Islamic biographical literature giving his dates, checked against the Kitab al-Sab'a's own internal dating to the early fourth century AH.
OpenIslamic intellectual history, Arabic biographical literatureDivinity Atlas Open Questions Register, First Edition