I've never seen the Stones with any earplugs in on stage, only Mick sometimes wear in-ear monitoring. So I would assume that after all these years, their hearing mustn't be that good anymore!!! Is there anything known about their hearing??
If he's from this planet (which nobody can assure), Keith must have some hearing problems after all the years performing: he spent a good part of the seventies playing three-meters away from an 300 Watt guitar amp blasting through a ten-loudspeakers box, and that can be, what?, 130-140 dB? Anyway it's volume enough to blow your head out of your body... Charlie has spent the same time playing drums with Keith's amps beside his kit, Bill amp's must be loud enough so he could hear himself despite Keith's volume...
It's no good pretending that loud noise of the kind experienced by many rock musicians is good for you...but there seems to be a lot of pot luck involved. Some folks get away with it whilst others don't. As regards the Stones...they obviously have experienced years of harmful sound levels on stage but probably aren't doing so today today. Moden monitoring and PA technology has much reduced the volume level on stage as experienced by the musicians. Guitarists for example no lomger have to stand in front of a a wall of Marshalls or Ampegs to be heard at the back ;^)
A friend of mine who works in London as sound engenieer told me that he met the guy who supplies ear monitors to the Stones, and that this guy told him that the boys are among the very few musicians who haven't had major hearing damages even after all these years of touring.