Susan, I also yearn to study in a disciplined, academic manner, but because of other responsibilities, it might or might not be in my future.
There are many ways to find a mentor or a teacher. Check around your area for local universities, where you can register for classes either non-credit or through a continuing education program. Check for local art leagues and art organizations. If portraits are your focus, go
here and
here and check out the artists geographically. Contact those close to you. I contacted Allan Banks, and it turns out he is coming to my town to teach a 3-day portrait workshop in December. We all have these opportunities, it's a matter of seeking them out. Even a basic drawing class will always be useful; read about sight-sizing on this forum, read all the art books you can get your hands, all of these things will help you learn, but the most important thing to do when you take a class or workshop is this:
Empty your mind of all that you know so you really listen to your instructor.
For some of us, this is not difficult to do
, and it will give you the greatest possible storage space for all the information you're exposed to. Later is the time to edit and choose what is relevant to your work.