Do you replace them as they get old even if they haven’t been subjected to an impact? After seeing the damage to Terrahawk’s lid after his RTA I’ve become somewhat paranoid about head protection.

They have a limited life. They degrade with both time ( slowly) and with UV exposure( more quickly)

somewhere round 5 years old is generally considered about the right time to replace them

Depends how they’re used/stored. I use my for communting and so it’s gets knocked about a lot. I replace every couple of years.