I say go for it. If it is something that you really want to do then you ought to do it. I do not think that you are too old. At the 141 school that I work at we have quite a few people who use there GI money to pay for their training. But like rickair said you are a little bit limited at a 141 school. The pace may be a little slower than your liking. We take you from 0 hours to CFI and it takes 1.5 years. That is flying 4 days a week which is dueable. So just do your research. Best of luck to you.