My teenage DD spends April to October in shorts everyday - grudgingly wearing official school uniform when necessary but this year, they are allowed to wear sports uniform instead as no changing allowed so she was in shorts daily. Only now, when it is starting to cool down, is she agreeing to take a tracksuit bottom in her bag to put on in the later evening (after dinnertime) when doing study - but she still goes to school in shorts and her fleece. (She does say there is a coat in her locker if she needs it, and her gilet is in there too if its cold).
She is perfectly happy this way. She has the layers she needs if she gets cold. But she just doesn't feel the cold the same as I do. (Already have my thermals out...).
There was 1 primary teacher who couldn't comprehend this and sent home a number of notes. (She also couldn't deal with DD's ASD/ADHD issues either - there were a LOT of notes that year!). But she eventually relented when she saw that DD had a coat with her daily, and a jumper in her bag, and that DD just wasn't cold even though most of the rest of the class were.
I also have a Cub Scout who comes in her shorts even now in November. We are meeting outdoors, and most are very well muffled up - but this particular Cub is skipping along in shorts and a light long sleeved top - she gets stuck into everything but is not comfortable if she gets too hot. And there was another one like her a few years ago - the only time he wore trousers was when we went on a hike when there was snow on the ground, but he was perfectly happy otherwise with bare legs.
My parents grew up in a time when there was less heating in houses, and all boys would wear short trousers until they got to 2nd class in some places (roughly aged 8), or senior school in others (roughly 12) - that was the norm. They would walk to school and home again, and just had to be hardy.