I hope I can help you here. Please understand though that no one online can diagnose or state anything with absolute certainty, all I can do is make my best educated guess based on what you wrote.
I can understand your concern about aging faster if your metabolism is speeded up but I assure you that is not the case. Time itself is not flowing faster, you are not going to experience the passage of one year in a month. The chemical processes of your body though may be increased, and unlike a machine, you can repair some damages; a motor needs outside maintenance. The motor doesn't age faster, its parts wear out sooner. Thats not the case in the human body, really. Arthritis and other degenerative changes don't happen sooner if we are more active. In fact, activity can increase health and abilities later on in life, making us more resistant to illness.
Walking is actually better for most people...running is very stressful on peoples knee joints, and a fast walk is a low stress way to burn fat and gain muscle. It has to be a brisk walk though, not an idle amble.
If you simply did not eat, your metabolism would slow down, making it very hard to lose weight because your body would think it needs to conserve what resources it had.
Fish oil pills are supposed to increase the levels of good cholesterol due to the type of fat they have (omega 3). Yes, your level of 33 is a bit on the low side, it should be over 40. There are other ways to increase the HDL also...you are dong some of them by losing weight and exercising. Here is a good web reference on HDL cholesterol: http://heartdisease.about.com/cs/cholesterol/a/raiseHDL.htm
I hope I was able to help, and good luck on your diet plan,