My Sting likes Nylabones, but the same advice would apply to any chew bone- when they get worn down too much or are too thin, then replace them. It isn't the concern about breaking a tooth because like your Aero, they usually gnaw at them, but that if the bone gets too thin or small, it can splinter and be a choking hazard. So, if I were you, I would let Aero enjoy his bones but check their condition and replace them as needed. I usually make the switch out of Sting's sight.
Sting Chance von Gaard AKC GSD 2/8/2006