Is it an expiration date, "sell by" or "best by" date?
Have you been keeping it in a cool, dry place?
Is it rotted, soft, or growing mold...?
Turtles eat carrion...let your nose, eyes, and fingers guide you. Bear in mind that some nutrients may be reduced or no longer present. Feed it as a protein supplement and snack along with other fresh, nutrient-dense foods.