Optimal Weight Committment

Well, I have for a long time seemed to not be able to get down to my optimal weight. Right now I have about 15 lbs. I really want to drop the 15 so that I will be a bit lighter running and at my age 55, the less stress the better. Currently I am running 3-4 days a week and around 15 to 22 miles. Running is as much for my head as it is everything else. I would likely have to be medicated or committed without it. :).............well, "slightly" kidding. Like what I have see here so far. It seems without logging or really paying attention I always eat a bit more, then plateau or start creeping up. Currently, 5'6" and around 160.