My mom (age 62) sits in the house all day and watches TV. How do I explain to her this isn’t healthy for someone her age?

As someone of a similar age, I can answer you several ways.

if her bills are paid, and the house is clean, and she’s not depressed, MYOB. She’s earned the right to do nothing. I would love to spend my days watching Mannix and Rat Patrol reruns. But I can’t. Lucky mom.

if she is depressed, then tell her (don’t ask her) that you and she are going to lunch. Pay for the meal. Talk about her. Maybe she’s grieving. Maybe her friends are slowly dying. Maybe YOU haven’t gotten as far as she would have liked you to get, and she blames herself.

There is the possibility that she is dying, and feels she has no one to talk to.

I’m hoping that it’s #1. while I agree with you, in theory, that it’s not healthy to stay indoors all the time regardless of age, your mom is an adult. She is living her own life.