You can be smarter than that. Kids Helmets Check out our pamphlet on child helmets . Replace any helmet if you crash. Impact crushes some of the foam, although the damage may not be visible. Helmets work so well that you need to examine them for marks or dents to know if you hit.
Most manufacturers recommend replacement after five years.
We think that depends on usage, and most helmets given reasonable care are good for longer than that. But if your helmet dates back to the 70's, it's time to replace it. Replace the buckle if it cracks or a piece breaks off. No one ever complains about the cost of their second bike helmet. Here is more information on that problem .