It sounds that he is developing quite normally. So, don't worry. There really isn't anything you can do to make him let go. Both of my kids didn't walk until 13 months. We played a game with my daughter. My husband and I sat across from one another and she would hold on and go back and forth and we would cheer and then we would just let her hold onto one hand and then we held on to her hips and then we let go. We just kept cheering and she was having so much fun, and then it seemed she just had the confidence to walk on her own.