How should I initiate conversations about planning ahead with my elderly parents?

My parents have recently (in July) turned 60 (mom) and 65 (dad). They are doing pretty well, but my mother has started to exhibit some early signs of possible dementia. I'm probably particularly sensitive to these signs because her mother, my grandmother, had very bad dementia for quite a number of years before she died. My grandfather on that side also required a fair bit of care for the last 8 years of his life. My mother and her siblings all coordinated that care. I am an only child.

Although my parents are in pretty good health now, I observed growing up (watching my parents take care of my grandparents) how difficult things can be if nobody has really talked about aging or planned ahead. I would like to start having these conversations with my parents while they are mostly healthy and before things get really dire. Do you have any suggestions for starting these conversations?

My parents have never had a will, although they recently signed health care proxy forms, each making the other their proxy.

Thank you in advance for your advice.