ANSWER: When a person comes to a knowledge of good and evil and understands that he, in his sins, is separated from God; when he comprehends the purpose of the blood atonement of Christ; when he understands the purpose of baptism as it relates to forgiveness and the singular nature of the kingdom (the church); when he has a deep desire to repent of his sins and to confess faith in Christ; when he is ready to commit a life of service to his Lord, then he is ready to be immersed! He can be nine or ninety! The restriction is not in age, but in knowledge and understanding!