https://www.consumerreports.org/health/bike-helmets/when-you...

Not necessarily:

But if you really like your old helmet—and it’s in good condition—one scientific study tested older helmets and showed that holding on to one for longer won’t necessarily put you at significant risk. Randy Swart, executive director of the nonprofit Bicycle Helmet Safety Institute and former vice chair of the helmet and headgear subcommittee for ASTM International, a nonprofit, voluntary standards-setting organization, says that his own helmet is “much older than that,” though he adds that there may be other good reasons to get a new helmet, such as more protective technology included in some newer models.