Welcome. I personally do not know of any chiropractors who have done this, but I know it has indeed been done. I've seen it posted on SDN several times.
I can say with fair certainty that U.S. medical schools won't grant advanced standing in any part of their curriculum based on your DC degree. My class has nurses, paramedics, and a PA and none gained advanced standing or obtained class exemptions. I think the subject emphasis in other branches of healthcare is often quite different, so they just make everyone start on the same page.
For initial screening purposes, medical schools care most about the undergraduate GPA and the MCAT score. For U.S. allopathic schools (M.D.), you're looking at an average GPA of around 3.55 and an average MCAT of around 29.5 for those gaining entry. For Osteopathic medical schools (D.O.), it's probably around 3.3 and 24, respectively. Keep in mind these are average numbers with a massive spread in the distribution (youll hear about people being accepted with GPAs of quite a bit below 3.0 and MCAT in the teens (usually not both together!); granted they are not the general rule at all but know assuredly that anything can happen. All medical schools seek to enroll a diverse student body so also keep in mind that there is more to you as a person than numbers so dont let anyone discourage you. Probably the most difficult part of your application may be explaining (convincingly) why you want to change from a very detailed branch of health care that required substantial training and sacrifice to more of the same.
Overall, make sure you have volunteer experiences and meaningful contact with physicans to make your application rounded. All U.S. medical schools require one year of general chemistry, physics, organic chemistry, and biology (all with lab) so check that you have all of those too. Your age and your previous endeavors matter less than your determination. The mean age of my medical school class is just shy of 24 (range: 20-51). We have ex-nurses, paramedics, Ph.D's, an ordained minister, a company CEO, and many other interesting accomplished individuals so you're in good company. Don't give up if this is what you really want to do. I, myself, was an imperfect applicant and I had a couple of red flags, but I worked with them as best as I could. You're no different. Good luck and, once again, welcome!