I was living away from home when I was 18 - college freshman. I spoke to my mother on the phone once every two weeks or so, and saw her about 4X yearly; she didn't know one way or the other where I slept, and it really wasn't any of her business at that point. Of course, had I asked her to make my travel arrangements for me, she would probably have felt that I was inviting her opinions, which I why I never did such a thing.
At that age I was pretty poverty-stricken; when we went to FL we drove down, slept in a tent on the beach and got most of our food from nightclub happy-hour buffets. Amazing what you can scrounge when you set your mind to it.
Oh, and on the original topic; hotels will sometimes waive the age limit if the guest is a member of the hotel's frequent-guest program (or the child of a high-status member who is willing to guarantee the stay.) Wearing conservative business-type clothing and paying cash in advance tends to work fairly well at the more budget-type properties -- dress older and you may not be questioned. (ID is normally asked for to verify the CC; if you pay cash you can be anyone you want.) The reason for the age limit tends to be about possible damages, so paying a large deposit can also work; best to call the hotel directly to ask what sorts of exceptions they are willing to make.