Planning my doctorate while entering kindergarten

The title is something I said on a friend's Facebook status. He had just posted his running distance and time, so naturally I commented and we started talking about our goals. I felt silly when I shared that my goals include not only a marathon, but a triathlon. I mean, I can't even run a full mile outside yet. I have so much work ahead of me, is it even possible? But then I thought about how far I've come. When I first started running on the treadmills at the gym, I could only run for 30 seconds. I slowly increased this, step by step, until I could run for 1 full mile (at a 15 minute pace). Then I moved outside. I could only run for 1/6th of a mile before I had to stop and walk for a while. But then yesterday I was able to run for a third of a mile, and was able to run again after walking the length of a block. By running a block and walking a block, I was able to complete 1.6 miles in 27 minutes. So I'm slow, I know. But the next time I go I'll run a few more feet. And so on and so forth, until I can run a full mile. And then I will keep going, because there is always room to improve. The thing that is hard for me to articulate, is why I run. I don't have an urge to run, like some of my friends do. I am finally at the point where I get exercise endorphins, but not so much that I crave them yet. I suppose I run because if you met me, you wouldn't expect me to be a runner. Runners are tall and lean, with wiry muscles. I'm short, and all curves. A lot of my goals in life I've done because someone told me I can't, or I wouldn't be good at it. Sometimes, those things have turned into my favorite activities. It's worked well for me so far.