What? Do you know the limitations of a helmet? They are designed and tested for falls from a bike with no forward momentum. Bicycle helmets are designed to reduce the effects of linear forces. The slow old man has a better chance of a helmet actually protecting his head in the manner that the helmet was designed. The old man's fall would most likely produce a small rotational force compared to the faster riders. Helmets are not designed for rotational forces, the forces that cause brain injury.

But, who knows. I am one of those knuckleheads that doesn't wear a helmet.