My husband and I went through this change in our lives about 12 years ago, and we found there were basic questions we had to answer before we could decide on such a big change....
The primary question is can you afford to? Can you reasonably expect to keep the basic standard of living you want? I'm not talking about how many times you get to eat out, but your expenses for your home and family. Is there enough resources for income to meet basic needs (food, mortgage, health)? Are you willing to cut back so your new income is sufficent?
Are you willing to travel more? If you don't live in the large metro areas, it has been our experience you have to widen your area of performance beyond the local areas to earn a living.
I think you stated your reasons for wishing to quit teaching very well. I also think you have much to offer schools on a per performance basis. Your experience as a teacher is money in the bank, I'm sure.
Age is certainly NOT a factor! You are multi-instrumental, with teaching, arranging, and composition skills. This is all marketable.
Since you have been a prefessional performer since 1983, you have the skills needed to promote yourself and your craft. If the answers to the questions above are yes, then I would expect you to be very successful as a full time performer!
PS...12 years ago, my husband went to being full time performers, and have never looked back. It is a wonderful life, though not what anyone would call "mainstream" Whatever you decide, I wish you luck! Keep us posted! My email is Rltpb971@cs.com