More seriously, you really start to feel "ancient" when your body goes from "new year, pretty much the same as old year" ... to ... "new year, who removed vital organs and bodily fluids while I slept last night?! The bastards!!!"
Of course, it is a classic trope nevertheless ... and I did start to feel ancient even 15+ years ago ... but once you start noticing real changes, then you REALLY get that feel (and you know more is coming, lol): https://youtu.be/MqBNSMbEzI0