Śatapatha Brāhmaṇa ("of a hundred paths") 7.4.2.38

7.4.2.38

tadāhuḥ | yatprajā viśvajyotirvāgaṣāḍhāya kasmādantareṇa 'rtavye upadadhātīti saṃvatsaro vā ṛtavye saṃvatsareṇa tatprajābhyo vācamantardadhāti tasmātsaṃvatsaravelāyām prajā vācam pravadanti

Here now they say, 'If the Visvagyotis (brick) is progeny, and the Ashâdhâ speech, why does he put the two seasonal ones between them?' Well, the seasonal ones being the year, he thus separates speech from progeny by the year, and hence children utter speech at the time (or age) of a year.