Clue: Animal that's old and can play dead (7)
Answer: OPOSSUM
Explanation: Definition: Animal
A charade of O ('old') plus POSSUM ("to play possum" is to 'play dead' – and do I detect a play on 'can' even if the person is wrong?) . Since POSSUM is an aphetic form of OPOSSUM, and the animal does play dead when threatened (hence the expression), as a cryptic clue, it is chasing its own tail. As a straight definition it can hardly be faulted.