I'm 55 and this will be the 5th winter I've cycled through. The last two days have been in the teens (farenheit). I think it's harder work, not least because of the extra clothing layers, so I think it's OK to adjust your milage down a little. In other words, I'm wondering if I normally bike 15 miles on a nice morning, would it be OK to drop to 10 miles on a really cold morn. Or am I just slacking?
Weather conditions here in central PA have been a drag this year. Lots of rain. I rode two days last week in the rain, temps in the low 40s, and at the end of that second day, I was dog tired. Part of the problem is that it's dark when I ride in and home, and visibility is poor in the rain (plus my night vision is crapping out more each year). As a consequence, I feel more bushed after those rides. Make sense, or is it just old age catching up? I'm hoping to get some easy on/off fenders for Christmas, because part of the pain of riding in the rain is having to clean the grit off everything when you get home.
My wife bought me some Endura rain pants last year. They keep me plenty warm in temps below 30. I have to say, though, that they're a little bulky and if it's a rainy day above 40 degrees, I prefer my Nashbar rain pants. Anything between high 20s to 40 degrees, a pair of tights and a base layer, even if it's long underwear, is enough to keep me warm if it's not raining.