I can say that I am enjoying my thirties to the hilt though there are slight hormonal changes in the thirties. During this stage your bone growth slows down, plus there is declining metabolism and depleted muscle mass add up to cause excess flab. It is imperative to do weight training or resistance training with attention to low or non-impact sports that preserve joints while building muscle and bone.
It should be 2to 3 days of interval training like running, walking or by using any type of cardio machine. Intersperse two minutes of moderate intensity workouts with one minute of all out exertion for a total of at least 30 minutes per session. Short burst exercises are much better than the continuous faster one. You can also for circuit training classes. Do not forget to add another day of about45-50 minutes of steady-paced cardio, such as brisk walk.
Do a little bit of weight training. This will help you to develop more muscle mass, something what you are starting to lose. The more muscle you can make the more efficient your metabolic rate will be.