Just to clarify some myths and misinformation: (most of this has been said previously in this thread but it is good place to summarize it all)
1) DO schools do not have a policy to favoring nontraditional over typical recent college grads. Most do have a "culture" of going deeper than just the numbers as they look for a clear, concise, and compelling narrative showing a strong pattern of motivation, commitment and achievement.
2) The difference in application mechanics, with grade replacement and science GPA not including math may account for a large percentage of older and nontraditional who apply. More applications from a demographic would likely lead to more acceptances from that demographic hence the older average student age.
3) There is no high end cut off of GPA and MCAT score for DO (sorry, I found this comment just silly). I have had students with outstanding records go to DO, for such reasons as geographic location (near family), setting (rural), holistic culture/attitude of osteopathy, long family history of having DO relatives or having DO as doctor, strong feeling for school at interview, etc. I would like to add I have several student with ridiculously high GPA/MCAT who decided against MD or DO and opted for PA, NP, etc due to time of training, debt load and family concerns.
4) Requirements for schools do vary on having a letter from a DO, but certainly shadowing, exposure to DO, etc, should be considered nearly a requirement.