Just a wee experiment:
Goldring NS1000s, noise cancelling off. 16 is last full volume. 17 I can just hear. 18 and above is silent.
Goldring NS1000s, noise cancelling on. 16 fine. 17 quieter but easily audible, 18 just audible, 19 just audible, 20 just audible, 21 just audible, 22 just audible. When I say 'just audible I really do mean borderline silent but there if I concentrate. The sound above 18 KHz is a lot queter than the hiss noise caused by the noise cancelling.
Sennheiser HD600s, same as NS1000s with NC on but no hiss
Goldring DR150s, same as HD600s apart from 19Khz seems slightly louder than 17.
Goldring NS1000s, noise cancelling off with Fiio E5 amp. Same as the last 3.
So it looks like I have significant hearing drop off at around 17khz but still got something up to 22 and the equipment can still manage it at normal volume, with the exeption of the unamped NS1000s in passive mode. I'll be 31 next week.
Edit: When not using FiiO e5, I was using the headphone output on my Mackie mixer. Goldring claim for NS1000s 15hz-20khz with NC off and 15Hz-23khz with NC on.