I have only ever been with a youth tour group, but when I went with them the guide talked a few times about how he had taken individual tours with older people, and I bet he would do it again on request. I don’t know how other tours are, but I had a great time on his.

At the very least, you could write to him and see what he has to say. Couldn’t hurt, anyway. (I hope that helps!)
References :
http://www.bigbrotherbackpacking.com