there is no prompt for the AACOMAS personal statement, so you can literally write about whatever you want. I'd say that most focus on 1 or 2 important aspects/events in their lives that have shaped who they are and who they have become, and maybe discuss why they are pursuing a career in medicine. This can be an extracurricular/volunteering experience, family obstacles, someone who has motivated you or supported you, or really whatever YOU think is important in your personal development as a human being and future physician.
You will hear people debate about whether or not you should include "Why DO" in the personal statement. Really I dont think it matters. Like many will point out, schools will ask you this question at some point or another, whether it be in the secondary application or the interview, so you might save that answer for another time and share something else that makes you interesting. It certainly isn't a bad thing if you include "Why DO" in your personal statmeent, but by no means will it be held against you if you choose not to. I never even used the word "osteopathic" let alone talk about why i wanted to go DO....and I have gotten off to a good start this cycle (check mdapps) with the DO schools. In fact, I used the exact same personal statement for MD and DO, excpet I added a little extra for the MD b/c i had more space to work with.
That being said, I am fully prepared to answer "Why DO" in my upcoming interviews as I 100% expect to be asked this question.
Good luck!