You have achieved less than you are capable of. You are slower, fatter and weaker than you could be. Why are you going through the motions? Do you really think that running for 30 minutes on the treadmill while paging through a Cosmo is helping you? Why don't you get out there. Run on the street. Take a new route today. Push yourself past that invisible barrier of 5, 10 or 15 miles. You are capable in far more than you think. All you need to do is break free of that nagging doubt that is holding you back. You can do it, I believe in you. The only questions is: do you believe in yourself?
Are you nervous before you run? Even a little? You should be. Every time. If you aren't, then you aren't doing enough. If you don't step outside your comfort zone then you cannot move forward. You will stagnate, languishing with all the other naysayers, pessimists and misanthropes. If that's where you want to reside, then fine. They will make room for you. Misery loves company. But if you want out and want to change then do it. No one is preventing you from becoming who you want to be except for you. Get on it. You aren't getting any younger.