I'm not going to read every post here but I'll throw in my two cents......with a preface.  I'm not overweight, never really have been, and am 36 years old.  The bottom line to loosing weight is figuring out how to burn more calories than you consume.  Certain diets or types of food tend to be more difficult for your body to process than other which is why there are so many different ideas.  What works for one person may not work for the next.  When it comes to exercise everybody is different too.  My wife has way more endurance that I do when it come to distance running but it is way more difficult for her to loose weight than for me.  I can run three miles a day, 3-4 times/week and loose weight.  Generally people do say that you need to do at least 30 minutes of exercise on a regular basis.  This I will concur with as I notice that once I up my workout times to 30-40 minutes weight loose (or ability to maintain) really goes up compared to 20 minutes a day.