My adult children live in different parts of the country and we don't see each other day to day. When we do meet up, it tends to be more of an "occasion" and I suppose I present my best self, because I want our precious time together to be good and memorable.
I'd say they don't get how my life has slowed down since I stopped working full-time to care, and am not hugely busy anymore. They don't get how I'm not as sharp mentally, I tire more quickly and sometimes have aches and pains for no specific reason. They seem to prefer a younger version of me, if she ever existed, who was more "cool" and engaged with life in general, and who had more of life's opportunities.
If one AC has moved back with you temporarily, maybe he/she hasn't seen how you and your life have changed as you've got older. You say your other AC is busy with their own life.
You know, I think sometimes they don't want to see it. Thinking back to my own parents, it was painful to see them age and develop health problems. I'm glad they didn't hide them from me though.
Perhaps generally in life, different generations don't mix as much as they did in the past, which would account for some of the lack of understanding.