I understand that 广 means wide or broad,大 means big or large, which should be used to describe the size of a place, but not for the population of people.
Does the above case of 广大青年 refer to all the young people over a large and wide place? And in how big and large a place is appropriate in this connection?
In Xi Jinping's 2023 New Year Address, here is again the phrase 广大青年要厚植家国情怀, and the translation given by the official Xinhua News Agency is "Youngsters should keep their country in mind", without any explanation about 广大.