I don't pretend to be an expert but, for me, the concept of Couguar is not only a question of age but also a question of attitude.
Normally, men are the "hunters" and the women are the "prey" and most of the time mature men are looking for younger preys. Women become couguars when they become the hunters and, most of the time, it implies that, due to their age and their sexiness, their prey is less attracted by them than they are attracted by him. Consequently, I can conceive that a very sexy and attractive woman will remain the prey at an older age and that she is not yet a couguar.
Men, if you had a chance to meet Demi Moore, who would be the hunter?