Well walking is good, does the walking cause you discomfort around the stomach area?
Exercise will help with aching joints, but it's a shame you don't swim too. Do you take Glucosamine? This supplement is good for healthy joints.
Try to do at least 20 minutes of Cardio 4 times per week and it's beneficial to do some weights too, as the more lean muscle you have, the more bodyfat will be used as fuel.
Regarding the apron, unfortunately, there is little you can do to improve it, it sounds like you have some muscle damage and you have probably lost some elasticity there too.