If she is your girlfriend, just ask her if she could give you a back rub. If it is just a friend then just casually ask them and give them a reason like your back is sore and hurts.
The guy ask the girl out on a date trust me a girl will most likely never ask guy out. Even if you asked her out on a date might pay the bill but other times your most likely goin to have to do that...
You don't. You are way too young to deal with such an older guy. At your age you should hang out with someone your own age. 17 year olds can play too many head games with you at such a young age....
It depends on the situation. Guys don't HAVE to ask the girls out, but they usually are the ones to gain enough courage to. Girls, if they really want to be with the guy, will ask them out. It isn't...