Our family had a fascinating experience some years ago when a relative visited from Switzerland, where she had lived since the 1950s. She was out of practice with English, of course. but even more interestingly, she simply did not know some "common" words because they post-dated her move abroad. I can't quite remember now, but I think it was either "roundabout" or "ring road" that threw her. It certainly emphasised the speed of change in the modern language - and in this case it wasn't just current slang that would die out within a few years but fairly well embedded vocabulary.
Certainly listening to old films is increasingly alienating, and more so for my children than me. Equally books I read as a child are as hard for my kids as, say, Black Beauty was when I was little. I'm not clear that this speed is not accelerating, and am in the mood for blaming globalisation. In some respects we may be generating a more widely understood and shared language across t'Interwebs, but it's a stressful experience to live through.
Personally I revel in it most of the time though! Playing with words, making up new ones, is such fun, and definitely part of the appeal of translating into Old English from Modern English, where new words are required for modern terms. I'm pretty sure it's good for my brain, like cryptic crosswords, in warding off dementia too.