The main difference between the PADI Scuba Diver and Open Water Diver certifications is the maximum depth a diver can reach and the level of independence they have:
PADI Scuba Diver
A beginner certification that allows divers to dive up to 12 meters (40 feet) under the direct supervision of a PADI professional. This certification is a good option for those who plan to dive primarily with a dive guide.
PADI Open Water Diver
An intermediate certification that allows divers to dive up to 18 meters (60 feet) with a certified buddy or dive professional. Open Water Divers have more independence and can explore a wider range of underwater environments.
The PADI Scuba Diver course is a subset of the PADI Open Water Diver course. After completing the PADI Scuba Diver course, divers can continue their training to earn the Open Water Diver certification.
The minimum age to become a PADI certified diver is usually 10 years old. However, divers under 15 earn the PADI Junior Open Water Diver certification, which can be upgraded to the Open Water Diver certification at age 15.