There's a sliding scale of interpretations on bb Shen Wei, but to me the mask and expressions and camera angles all make him look like a pudding-faced bb. Like, he's clearly pubescent, but he's still (very) young, and the way his insecurities are played is very ... young-seeming. In any case, he must've been a child soldier at some point, which would be an interesting avenue to explore in fic – he's really been put through the wringer, no wonder he has troubles relaxing and trusting people and letting other people share the burden! (Zhao Yunlan, give him a hug and bring him to a psychologist.) In the modern era, he's hit with the double whammy of being from the far past and being Dixingren, and yet not being able to tell anyone about either of them. He sets himself apart from his people due to his position of authority, and if he really were from 10k years ago in Earth time, he'd be illiterate (writing was only invented ~8k years ago), and definitely not speak anything legible to modern ears. Hell, he predates wheels, agriculture, and silk. Obviously time on Haixing works differently, but he really is from another place and alien in two ways he must keep secret. Of course he'd cling to the only remnants of Home that he has (Zhao Yunlan, Ye Zun, maybe Da Qing).