Tā chéngnián hòu cái zài Tiānzhǔ jiàotáng shòuxǐmìngmíng.
He was not baptized and given his Christian name until he was an adult, at the Catholic church.
Tips
culture
受洗 alone means 'to be baptized'; adding 命名 (mìngmíng, 'to name') captures the second half of the rite — receiving a baptismal name. The compound is most common in Catholic and Orthodox contexts where naming is part of the sacrament.