Jeff has it pretty close. It is just about the time kids are "independent" but Mom has spent her whole life doing for others.
45 or 50 is right around the corner
She starts staring at little wrinkles on her hands and putting on her reading glasses to stare at tiny crow's feet in the mirror. She starts waking up and going to sleep at night asking "What about me?" and "When is it my turn?"
When they go to an IC to discuss this, they are told "Now is your time and you should just go with it"
They want to feel that passion they haven't had time for in years. Someone at work has noticed them, talked to them, encouraged them. The LBS doesn't see it coming, it has been behind the scenes, covered up, but growing for months or recent years and can no longer be denied.
BINGO !!! The bomb.
Maybe instead of celebrating a particular year mark, just celebrate the awesomeness of still being.