Someone who is in their late twenties/early thirties who is single but established in life. They are well into their professional career, have a fancy car and own their own house. Their friends around them are settling down and having kids but a box set ready person remains single but is desperate to meet someone and quickly settle down so they can catch up with their settling down friends.
This person is "box set ready."
"My best mate has just got a raise at work and life is going great but she is box set ready!"