Ask your priest about this. He may need to ask his superior. He’d need a Baptismal Certificate, and information pertaining to Holy Communion and Confession, also, his mother’s permission. There was a lady at my chapel whose granddaughter, also age 12, wanted to become Catholic. Her mother had married a Protestant and given up her religion for the Baptists. Unfortunately, her parents would not consent saying she had to attend their church so long as she lived under their roof. So the priest could not allow it.
Hopefully, your young man’s parent feels differently!