Depending on the country you might actually be legally obligated to take care of them unless you can prove serious crimes like physical/sexual abuse
So my educated guess would be you never have to actually care for your parents, but I'd be curious if any other countries actually will order children to nurse their parents.
https://en.m.wikipedia.org/wiki/Filial_responsibility_laws
I get that “no free country” can have many meanings, but these laws certainly exist in countries people call free.