When you are pregnant there are huge physical, mental & emotional changes. The same thing is true with ageing. The body is a truly amazing system, but like a car engine, it wears out through time & constant use. Skin thins and becomes less elastic and more fragile. Fatty tissue just below the skin decreases. Wrinkles appear. Your image of yourself is completely different, but internally you think you are the same person. Your organs & muscles start to fail. Bones shrink & weaken. Memory & thinking becomes less reliable. You can't hear or see as well. The Mayo Clinic gives much more detail - https://www.mayoclinic.org/healthy-lifestyle/healthy-aging/in-depth/aging/art-20046070
There are huge psychological changes to deal with too, often causing low self esteem, anxiety, depression & frustration. It isn't easy to adjust to role & lifestyle changes, grief at the loss of partners & friends, family relationship problems etc.
Such massive change can result in the necessity for a huge adjustment from the individual. You lose control & independence by degrees. There is frustration at not being able to do things you previously could. You have to rely much more on other people to help. Ultimately you may need daily social or nursing care.
Some people are lucky. It's a bit of a lottery. My father, who smoked Capstan full strength from early teenage years & lived to be 88, was very fit until he was diagnosed with cancer in his 80's. He reckoned not to know what a headache or backache was. Others develop chronic conditions very early on in their lives.
I was part of what is called the "baby boomers" & "sandwich generation", who physically and financially supported both their children and their parents, as well as juggling jobs and careers. It was very high stress at a time when I had anticipated being able to focus on myself, my husband & my professional career.
My generation remember grandparents being cared for by their immediate family. We also felt a strong responsibility to care for our parents, but even then most women worked, so it was very difficult. Especially as families were much more geographically dispersed than previously. The world has moved on & attitudes have changed. I think that we have to question whether family responsibility for their elderly is possible or even desirable or practical today. Actually I for one would not want to live with my daughter & her family. I value my own space, routines & indepedence. I value the peace of my life.
Ageing in one form or other comes to us all. So you would think that we would be prepared for it. Even more importantly, you would think that our politicians would have planned for the impact of ageing on the health & social care system decades ago. After all demographic trends are known well in advance from birthrate statistics. But our political system isn't geared to long term planning & policy implementation.
Over 30% of people over 65 live alone in the UK. Roughly a third of those are lonely. 40% of people over 65 have chronic conditions. Unless we address the problems of old age properly & fund solutions these statistics will not improve. It's in the interests of everyone to push hard for change.