Non-traditional graduate student?
A PhD in mathematics education is a highly sought after qualification these days, although it isn't clear to me whether the long term prospects over the next 20+ years are particularly good for any academic career.  

Getting a PhD late in life is certainly possible- two of my colleagues in a relatively small mathematics department got their PhD's in mathematics well into middle age after other careers.  

Given that you got your bachelor's in math more than 20 years ago and haven't done anything in mathematics since then, you may have some difficulty doing mathematics at the level you were at when you completed the bachelor's degree and without current letters of recommendation you may have a very hard time gaining admission to a graduate program.  

One approach that might help you to reestablish yourself in mathematics and get into mathematics education would be to start taking graduate level courses as a part time student.