18 Again!

Jack Watson is a millionaire playboy and businessman who is about to turn 81 years old just as his grandson David is about to turn 18, but Jack laments his old age and wishes to get back to his teens once more. When an accident switches their souls, Jack gets to live his grandson's life and all that it entails: school, sports and romance. Unfortunately, David gets the "short end of the deal", as not only is he trapped in his grandfather's 81-year-old body, but he is also in a coma. The only one who knows the truth is his longtime friend Charlie, whom Jack was able to convince by recounting experiences only they knew.