Do they allow aerobars in organized century rides? I would think that the benefits of riding with a strong group far outweigh the benefits of aerobars. What he needs to do is show up in good shape and ride in the stronger groups. Most likely his pace will be in the 21-23 range...which should easily get him home sub 5 hours. If he's doing a solo century, then yes I'd say he must have aero bars. But I do not recommend them on an organized ride.