I hear Mr. Xi Jinping in his address to villagers spoke 老少边穷地区 in the fourth tone (i.e., 少 as 绍）, but I think he might have made a mistake here, out of instincts, without any real understanding.
It should be pronounced as the 3rd tone, i.e.
少 in 老少边穷地区 refers to 少数民族自治地区.
BTW: 老少 (pronounced as
lǎo shào) is another word which means
the old and the young. So pronouncing
lǎo shào biān qióng would be quite confusing.