The reason Prince George only wears shorts is because of tradition and his age.
Up until age 8 years old British and UK kids according to tradition are only supposed to wear shorts and then after 8 or by age 8 they can wear pants or trousers.
Since Prince George is now 8 and about to turn 9 he can wear trousers or long pants instead of his shorts.
Boys should not stop wearing shorts unless they want too.
However some boys stop wearing shorts around 8 years of age.
But some boys prefer to continue wearing shorts in the summer and warmer months and even guys can wear shorts if they want too.
As for the British.
According to British tradition, boys do not wear long pants until they reach the age of seven or eight.
A pair of trousers on a young boy is generally considered middle class.
Men's shorts are not really getting shorter but there are short shorts available for men and those types of shorts may be getting shorter but regular men's shorts are typically the same length they have been for a long time.
Short Shorts for guys are typically called hotpants.
There are cargo shorts, chino shorts, Bermuda shorts, hiking shorts, and more.
Khaki's are traditionally made of 100% cotton twill fabric, but other materials are sometimes used.
It is OK for guys to wear shorts.
Shorts are made for both men and women as wells a boys and girls.
There's no gender or age that you should stop wearing shorts.
I'm a guy and I wear shorts all the time in the summer and I could care less what anyone else thinks.
If you're comfortable wearing shorts you can and should wear shorts whether you're a guy, woman, boy or girl.
I see lots of guys out and about wearing shorts and they make and sell lots of men's shorts.
Some guys have issues with their legs being seen but there's nothing to worry about.
If someone thinks you look bad in shorts as a man then that is there problem and nobody else's business.
I would not worry about it and wear shorts when you feel comfortable.
Even some men police wear shorts when it's hot out.
Wear what you're comfortable wearing and forget about what other people think.
Dress how you want as well and if someone makes fun of you just ignore them.