I'm 40, and I've been programming professionally for two years, but I'm currently trying to get a better paying job. I find the main stumbling blocks are inability to "talk shop" well and lacking experience in highly specialized skills. Talking shop convincingly is difficult because I haven't had much experience collaborating with other programmers. I imagine you would have the same problem. Employers expect you to have all the correct terminology flow right from the tip of your tongue. The other issue is that a lot of employers seem to be looking for a lot of experience in a very particular area, which an inexperienced programmer is rarely going to match. You have to program for many years on many different projects to have a good chance of matching what someone is looking for.
Age itself, as far as I can tell, is not an issue at all. At least, not at 40. Although I know there's some very vociferous people on Slashdot who will tell you otherwise.