A childhood belief about church

When I was in primary school, one of the local ministers or priests would visit weekly to give religious instruction. When I was about 11, a catholic priest came and talked to us about catholicism. Afterwards, he asked if there were any questions. I stood up and asked "How old do you have to be to become a catholic?" I wasn't embarrassed at the time but I still go red when I think about it now. You see my older sister had converted to catholicism when she was about 12, (and was thinking of becoming a nun) so I thought it must be nearly time for me to do the same.