Life span of platelets is:

Platelets are small, granulated bodies that aggregate at sites of vascular injury. They lack nuclei and are 2–4 μm in diameter. There are about 300,000/μL of circulating blood, and they normally have a half-life of about 4 days. The megakaryocytes, giant cells in the bone marrow, form platelets by pinching off bits of cytoplasm and extruding them into the circulation. Life span of platelets is around 8-10  days. Reference: Ganong’s Review of Medical Physiology T W E N T Y - F I F T H   E D I T I O N page no 555