"How are you initiated into Christianity?"

Christians must go through Baptism to be a proper Christian. There is no specific age but most Baptisms take place at the birth of a child to a Christian couple.

"How are you initiated into Sikhism?"

Sikhs' must go through Amrit so they can be apart of the Khalsa (free, liberated). Amrit is a sweet water that Sikhs use as baptismal water and a sacred drink.