Holy Mother of God.
That means Du Heng has been alive for a very long time. No wonder Xiaochong hides from him the second it catches Teacher Du's scent.
Well, based on Xiachong habits and his mention on his mother nagging him, he's only relatively slightly younger (he was also born before Old World ended).
The task force actually have a relationship with someone from the Old World. Du Heng could probably answer all of their questions...too bad his memory is shot, lol.