Question: how to calculate age for upanayanam?
Answer: Upanayanam as per Vedic rituals should be done at the age of 7 or 9 or 11. 13 is ok, but after 16 it is not permitted in Sastras. Since he is 9, its the best age to perform brahmopadesam. and this Year during the month of Masi, Panguni are the best months to go in for Upanayanam.