Dude, you should at least wear knee warmers. Riding in shorts in cold weather can be hard on your knees. I cover my knees for any temps lower than 65 F. You may be young and fearless, but things like that will catch up with you when you get older.
Tarwheel, you're right. At 43 the inability to get my legs to loosen up on cool/cold ride commutes is the most noticeable development in my ride. I find that I'm more tolerant of the cold but, even in cool temps my legs are very reluctant to loosen up where they used to be good to go right off the bat. I've been thinking of knee warmers but haven't gotten around to getting them yet. Maybe I'll do that soon. I've also noticed that my knees ache more than ever after a ride on my single speed MTB-I've come to the realization that I will have to go back to a geared bike soon.