Concept:The pattern “too + adjective + to + verb” means “more than enough/too much for a purpose.”Explanation:The sentence is: “Isn't that girl … old to play with toys?”The structure “too old to play with toys” is correct because “too” shows that her age is more than suitable for playing with toys.“as,” “so,” and “very” do not fit this “to + verb” structure naturally.Answer:C. too