Here’s an example of how I might dress for a ride to work when it’s in the 40’s. That’s degrees farenheit, not the decade.
It was about 48-50F in the morning when I left dressed as you see here. On bottom, I have wool knickers and long socks that cover my knees. I wear the knickers all summer, but generally not when it’s below the 40F. On top, I wear a cotton T-shirt and wool jersey. I use a helmet with a visor, long fingered gloves, and goggles to keep the wind off my eyes in cold weather.
Women have it easy: capri pants, leggings, and tight fitting shirts are all well within the range of accepted “normal” clothing. Not so much, for boys.
As is usual, layering is the order of the day. The temperature dropped down to around 39F by the time I left work, and I was prepared with an ear warmer head band thing, and a wind proof shell for my top. Everything else was the same. I wear the same windproof shell and wool jersey down to about 20F without problems, but I need more extensive head covering at lower temperatures.
Wool is an excellent fabric for use when bicycling, anywhere from cool and dry weather, to light drizzly rain. It’s warm even when wet, it breathes well, and there’s almost nothing you can do which will make it stop smelling like a sheep. Although all my wool clothes claim they require dry cleaning, we just wash them in the normal washer using Kookaburra Wool Wash, and let them dry in the air instead of the drier. They require washing only very infrequently, even with constant use in sweaty conditions.
It’s best for everyone to discover for themselves what they need to wear at various temperatures on the routes they usually take. Factors such as how windy it is, and how much effort you make when cycling also make a big difference. For example, when it’s colder out than I expect on my way home from work, I’ll often take the “mostly uphill” route home, where I require more effort (and heat myself up more) to go more slowly (with less wind to cool me off).