It's not quite clear to me whether you're thinking about boarding a horse or keeping it at home.
You say your mom is very experienced with horses, but not in shape to ride. Assuming you are thinking of keeping the horse at home, will she be willing/able to take on the day-to-day care of the horse? Will she be wiling to do that even after you go off to college? Indefinitely? There are just so many cases of teenagers getting horses then leaving for college and the horse just sits in the pasture, acquiring bad habits or bad health and becoming virtually impossible to sell. This may not be the best time in your life to commit to a horse. Also, (again, assuming you would be keeping him at home) a horse really needs companionship. So will you get two? Or a goat or something?
If thinking of boarding, at least you don't have to worry about feeding, etc. (presumably you would go to a full board barn), but will your parents be willing to continue to pay board on a horse you're not using because you're at college two hours away and have homework, exams, etc.?
I would definitely advise you to wait because you're at a point in your life when things are about to change radically. Going off to college, maybe meeting someone, getting married, having kids (no, I don't think all those things are going to happen in the next year, but they can happen in the next 10 or 15 and horses often life to the old age of 30 these days!). It's a great, exciting time in your life and it's great that you have this opportunity to have a horse of your own, but not really fair to the horse. Unless, as I said above, your mom is willing to shoulder the day-to-day care of the horse no matter what.