Gobhilagrihyasutra 2.10.4

2.10.4

ā ṣoḍaśād varṣād brāhmaṇasyā 'natītaḥ kālo bhavaty, ā dvāvim̐śāt kṣatriyasyā, ''caturvim̐śād vaiśyasya;

Until the sixteenth year the time has not passed for a Brâhmana, until the twenty-second for a Kshatriya, until the twenty-fourth for a Vaisya.