actually as long as we're talking about realistic expectations of ageing, the nature of social media decontextualising people's personal posts has absolutely given some of you guys a false and potentially dangerous view of how your body is expected to change over time. I semi frequently see people sharing or repackaging commentary on experiences with disability as if it's an inevitable part of getting older. and like, yes, as you get older you are likely to develop new conditions, injuries or disabilities, but you need to understand your body's baseline well enough to identify those changes and interrogate them.
e.g. if you are seriously having such bad joint or back pain in your 30s that it hampers your day to day activities, you need to take that seriously. that is not 'just ageing', that's potentially an indicator of an underlying condition, unaddressed injury (which is quite common but will get worse if you don't notice and take care of it) or daily habits (poor posture, poor diet, sedentary lifestyle) causing cumulative damage to your body.
I know plenty of 30+ and 40+ year olds who are not especially athletic but who can still climb up and down stairs with ease, sit on the floor and get up again without discomfort, have floor or shower sex, ride a bike, wrestle a dog or a kid, climb a tree, maybe even do a handstand. there is no shame at all in developing pain or mobility issues which limit the kinds of things you can do comfortably, but it doesn't serve anyone to pretend that those changes are bound up with reaching a certain age. even in your 60s and 70s and beyond you should notice if you start feeling a new kind of pain or physical limitation. don't dismiss this shit just because someone told you "yeah that happens when you pass 30"