The older you get, probably the tougher it is to adapt too. Wearing hearing aids is very strange for the first little while since you're hearing all kinds of strange things again. For me everything seemed sharper/harsher initially but that's just because it all had been so muted for so long! It took me months of continuous wearing to get used to the sound so that it now sounds unatural to not be wearing them. He really needs to put them in when he wakes up and take them out for the shower/going to bed and thats it. If he only wears them occassionally, he'll probably never get used to them (my dad/grandpa had the same problem).

His audiologist can also set him up with a "training" program in his hearing aids that softens the amplification while he's getting used to them and after a few months go back to a more normal program. If he's not happy, have him talk to his audiologist...high end devices are highly tunable!