if your talking about the recent chapter... and the guard standing at the table across from hashirama, that is a mist ninja... u can tell by his cloths and that he is standing behind the mizukage...
It could be his dad. That guy is definitely younger than Hashi and who knows, he could of found love when he was older... Look a J-Man RIP he had no one and he was in his 50's
Only asking because the 1st and 2nd mentored the 3rd when he was a child. 1st died leaving the second to rule. 2nd died leaving the 3rd and the 3rd was in his twenties when he mentored the sennin as children. It looks as if the guard is the same age as all the 2nd kages standing behind their first.