I don't know how to distinguish between normal forgetfulness and dementia. Regardless, I think it would be good for us all to have some contingency in place, in case we aren't mentally able to manage for ourselves.
My FIL has done planning for his estate, but there was nothing to deal with him being mentally not with it. His family is attempting to do the annual required minimum distribution from his IRA, in order to avoid a fine from the IRS, and it has been a problem.
They attempted to get him to sign a required document, and he was having none of that. He thinks he will lose his citizenship, and they just want to take his money and abandon him.