Though state laws can differ, in general a juvenile cannot enter into a contract so thus cannot be a sole owner of a motor vehicle. A minor cannot normally own property until turning 18 and becoming an adult. The teen's parents technically own the property in most cases. For example if a parent will co-sign on a loan for a car, the juvenile can buy a car, but the parent will be the legal owner.
Even those states that will permit a teenager to register a car will normally require a parent or guardian to sign on any legal documents or contracts since they are still a minor.
The Alabama driver manual does not state at what age a person can register and title a car in their name. To find out the minimum age requirement for vehicle ownership in Alabama, the title only in their names and not the child and parent, you will need to contact the AL Motor Vehicle Division.
If you or your son is in need of Alabama auto insurance, follow this link.