Devibhagavatapurana 7.36.21

7.36.21

kathitaṃ tanmayā sarvaṃ nāto vaktavyamasti hi |
idaṃ jyeṣṭhāya putrāya bhaktiyuktāya śīline ||

This Brahma Vidyâ (science of the knowledge of Brahma) is to be imparted to the eldest son, who is devoted and of good character and to him who is endowed with the good qualities as enumerated in the S'âstras and not to be given to any other person.