According to the Old Book of Tang, Xue was 25 when this happened. See Old Book of Tang, vol. 73. However, based on his death year and age given in Xue's biographies in both the Old Book of Tang and the New Book of Tang (which are used here), he would be 27 in 649, and when he was 25 in 647, Emperor Taizong was still emperor. See also New Book of Tang, vol. 98.
