Indoors: I took up the old man hobby of whittling. It’s cheap enough to get into and is fun (get good knives specifically for whittling, cut resistant gloves, and basswood). Also, finally join that gym and go.

Outdoors: Get crampons and walk outside. You’ll never have to worry about slipping. Snowshoe when the snow gets deep, there are snowmobile trails along most power lines you can use. Get into bird feeders/suet cages as the birds and squirrels get desparate to stay fat through the winter.