My dad became a godfather at 11- granted that was 58 years ago, but I think the idea of a godparent is to be there to guide the child as it grows up and try to ensure that he or she is taught about the church or religion they follow. I know this is a slightly out-dated role and very few godparents are ever asked to ensure their godchild attends church, but it does mean that age shouldn't come into it when choosing a godparent as long as you feel that the person you choose is able to be a good role model for your child.