How old was the man for whom Āryabhaṭa numeration is named when he wrote Āryabhaṭīya?
Aryabhata: Aryabhata (IAST: Āryabhaṭa ) or Aryabhata I (476–550 CE) was the first of the major mathematician-astronomers from the classical age of Indian mathematics and Indian astronomy. Aryabhata:  His works include the "Āryabhaṭīya" (499 CE, when he was 23 years old) and the "Arya-siddhanta".
i don't know