Katrina is right in a way. In my class at LMU-DCOM, we have people from their early twenties up into their forties. Really, you can take a shot at medical school anytime you want, but I would take a look at why you want to be a doctor.
If you are wanting to make a change for the sake of money then it is a poor choice. You will be so far in debt when you are done that it may take you too long to recover from the cost of attending school. If you want to go to medical school because you can't think of anything that would fill that void that is in your life, then go for it. Trust me, the amount of studying and learning you will do will fill all your voids and more.
I won't be done with medical school until I am 32. My kids will be in junior high school (or maybe high school) by the time I finish my recidency and really start to work, but I can't think of anything I would rather be doing with my life right now.
So if you feel you are up for the challenges of medical school, then forget about age and give it a shot!