My realisation of 'old' age, apart from making involuntary noises every time I move or talking to myself in shops, has to be music. I've reached that age of non compliance with new music - it's all rubbish.
When I was a kid in the 70's I knew of the Beatles but they seemed really ancient and black and white. I didn't comprehend that they only split up just four years before I was born. The Beatles were not 'in my life' (see what I did there) whereas Iron Maiden definitely were and now they are thirty to forty odd years in the distance. I know they are still going, but my days of Heavy Metal are limited now to nostalgia bouts and very little to no head banging. Nowadays, I love them both, but much prefer The Beatles. I've matured... ish.
I'm also grumpy, but reaching that age (just one year off the big 50) where it is acceptable. Not sure when I'm supposed to start being racist though...