I have a son, Jordan, 11 years old, that was certified at age 10. He carries a Jr. Open Water Certification (PADI), and has taken to the sport of SCUBA like a fish to water.
Like Rebecca said, you must be entirely sure that you are at ease in the water. Jordan's instructor asked for a meeting with him before he would agree to enroll him in the certification course, mainly the instructor wanted to evaluate my son, to get a feel for his maturity level.
Best wishes to both you and your father on getting certified, I know that I have a great time diving with my son whether it's a short trip to one of the local lakes, or like our most recent trip to Nassau and Freeport, in the Bahamas.
Oh, there is one more thing to remember, you are going to have to read a pretty healthy amount of material while studying for your certification, but the rewards are well worth it.