I have a pet theory about the older women part: they're a remnant of gender segregation. When teaching was one of the few professions available to women, the lack of competition from other lines of work made such teachers cheaper and more plentiful. I had a similar experience further south. Though, notably, many of my best teachers were older black women. I suspect combined gender and racial segregation led to that.
On the other hand, the best and brightest women used to become teachers. Nowadays, those women will typically go into other professions. Why deal with teaching when you can go into law or medicine or engineering.
My mother, a retired high school science and French teacher, thinks that part of the reason we have a dearth of excellent teachers is because women are now doing other things than teaching.
This is a point made by the education historian William Reese. It is also suggested as a partial reason for our lack of 'professional' respect for educators because teaching was considered a 'female', caregiving job (that men wouldn't really begin entering until the 1970's).
