I don't have an age limit for guys but I would say that it seems to be younger guys who are more likely to no show. I'm currently in an area where there are a lot of students and I had 6 not turn up yesterday (out of 8 bookings!) This is the second time I've toured here and I experienced similar last time.
Yesterday I had a call from a guy who asked where I was. I told him the hotel and asked if he knew where it was, he said no but he would find it and could he book for 2pm. He sounded dopey as fuck. So I said Why don't you look it up on Google maps and see if you can get here easily, and call me back if you want to make a definite booking.
5 minutes later he called back again. I gave my standard greeting, he then went into the exact same speech as the first time, asking me what hotel I was at. I said "We've just had this conversation 5 minutes ago, why are you calling back if you haven't looked it up?" "Erm.... ugh.... Erm... What hotel you at?"
So not only was he ringing multiple sex workers, clearly, with the intention of making multiple bookings then deciding which one to go to, he couldn't even keep track of who he'd already phoned! Dick.

Paris when your friend takes the bookings, does she have an instinct about who's going to turn up and who isn't? I have found my instinct on this is getting much clearer and if I have some doubts I'll now make them jump through an extra hoop, e.g. I'll say sorry there's someone at the door, can you ring me back in 5 mins to confirm your booking?