The long run ahead

I'm a runner too. An even later bloomer than you. I didn't start running until I was 53. I had always hated it. Once I started I grew to love it. My longest distance to date is a half marathon, so this is my advice. When I'm attempting a pr distance, I like to think of it in terms of time. I tell myself I'll run for an hour, or 90 minutes, or however long I think it will take. I find once I've run the time, I've either met or beat my pr distance. A potential mistake I see you making is not eating enough carbs. I understand why you're cutting down on carbs, but unfortunately your running will probably suffer. The good news is because you are a runner you can eat more carbs and still lose weight. Here's a link to a helpful article about carbs and running. http://www.livestrong.com/article/536766-how-much-protein-carbs-do-runners-need/ You've heard about carb loading before a long run. There's a reason for it, but you have to start carb loading a few days before to get optimum results.