Early ripe, early rotten
Early ripe, early rotten,and Soon ripe, soon rotten.
Prov. A child with extraordinary talent or intelligence will probably lose those qualities by the time he or she grows up. Jill: Philip was such a fine young boy; I'm surprised he's become such a good-for-nothing adult. Jane: Early ripe, early rotten. Jane: You must be very proud of your little boy. He seems so mature for his age. Ellen: I'm afraid it won't last. You know what they say: "Soon ripe, soon rotten."