If you are really serous about improving your golf you should visit the online Titleist Performance Institute. The Golf Fitness Section provides you with articles covering every aspect of golf specific fitness. Everything from Strength training for golf to Stability, Mobility and Cardio are covered. If you are interested in understanding more about your golf swing and your body then Click here for more its brilliant. Here is a great article for senoir golfers Click here and hear what Arnold Palmer and Roger Fredericks have to say about Arnold's Flexibility program.
Below is a great stretch exercise by Mike Pedersens which will help you improve your hip rotation, essential for more power and consistency.