The issue would be why invest the resources in training a 40 something who has 20 years less of a working life ahead of her than and 20 something? When I say resources, realize that student tuition is a drop in the bucket compared to the real costs to educate a professional of the type you are discussing.
I also wonder if an admissions committee would worry that this is your third career change, so it will be important to articulate why this time you are sure. Its easy to say you made a mistake the first time around, but the second time too?
that's a very valid point. A friend of mine has gone back to school to get her pre requisites to apply for medicine. She's been told by 3 schools if she's looked into Osteopathy. She was like "Osteopathy? what's that?" Finally after the 3rd time she was asked, she asked back in return if they were asking this because of her age (42). They said in not so direct way that yes, it's because of her age.
Osteopathy's not as regulated or as popular so it would be easy for her to get in.