Lu Xiangxian's biographies indicated that he served as the sheriff of Luoyang County during the reign of Emperor Taizong's daughter-in-law Wu Zetian, while the official Ji Xu served as the deputy minister of civil service affairs (699–700) and so Xiao's marriage probably occurred during that time. See Old Book of Tang, vols. 88 and 186, part 1; New Book of Tang, vols. 116 and 117.
web.archive.org
Xiao was described to be in his 80s when he died in 749. Given the Chinese calculation of ages, he thus could have been born anytime from 661 to 670. See Old Book of Tang, vol. 99Archived April 19, 2008, at the Wayback Machine.