It depends. You could potentially do a post-bac. A lot of programmers have taught themselves though. You should read about this guy Con Kolivas who did all this kernel hacking even tho he's an anesthesiologist with no (or little, I'm not sure) formal CS training.

The trick is you have to really want to do it. Continued interest in what you're doing will keep it going. That's why I didn't program for years was because I had no interest but now that I have a firm grasp on what is wrong with computing and what needs to be changed, my desire to do something about it is pretty high.