Skandapurana 16.105.54

16.105.54

triṃśatkalpaiḥ smṛto māso varṣaṃ dvādaśabhistu taiḥ ..
anena varṣamānena tadā brahmā'ṣṭavārṣikaḥ ..
ānītaḥ somarājena somanāthaḥ pratiṣṭhitaḥ .. 54 ..

A month is considered to consist of thirty kalpas, and a year of twelve such [months]. / By this reckoning of years, Brahmā was then eight years old / when brought by the moon-god, and Somanātha was consecrated.