1.) If you don’t actually care about osteopathy, you will regret chaining yourself to it at some point when MD becomes easier or more appealing a path.
2.) Never, ever, ever sign with a medical school when you haven’t even set foot in your undergrad program yet. I have no idea how you don’t see how predatory/opportunistic the offer even is.
3.) Going into med school younger and with less academic/research/clinical experience will be a hindrance to you, not an advantage. The extra year of schooling is absolutely a worthwhile price to pay.
In short, as a fellow aspiring DO I think this would be a major mistake on your part, one that could tamp down your chances of having the career you actually want.