I suppose its an individual thing really. We are all different.
I still care about what I wear. And I like to buy some new styles every year. I have told my daughter she has permission to access my account and buy me new clothes if she ever sees me wearing dowdy anoraks or suchlike.
I think some older people see no point in buying clothes if what they have is still good, regardless of whether it looks outdated or not.
Forgetting where you left your keys does not mean you are “losing it”