What is the oldest-recorded language of Iranian branch Indo-European family?

The oldest-recorded language of the Iranian branch of the Indo-European language family is Old Avestan. It is a language that was used by the ancient Iranian people known as the Avesta. Old Avestan is primarily known through the texts of the Avesta, which is a collection of religious texts of Zoroastrianism. It is believed that the Avesta was composed between 1500 and 500 BC, making Old Avestan one of the oldest attested Iranian languages.