Get a Gravelbike or put Gravel tires on your mountain bike and keep riding all winter. Where I live the singletrack is some version of snow, slush, mud, or ice all winter long and is therefore impassable. That’s when I slap some gravel tires on my mountain bike and ride pavement or any dry gravel I can find. The right gravel tires (I use Panaracer Gravel Kings SK 700×43.) roll surprisingly fast on pavement. A short-travel full-sus or hardtail mountain bike makes a pretty good Gravelbike. I also walk, hike, and cross-country ski to mix things up. With the right clothing, riding in sub-freezing temperatures is do-able. I’m also 62 and I ride 4 to 5 times weekly. Start slow and build up. Before long, riding every other day will seem easy.