(SPOILERS)
math is an important subject
The age diff between mo xuanyu and wei wuxian is most likely 9 years.
wwx was 22 when he died during the 1st siege of the burial mounds and a year after that (22 +1 =23), mo xuanyu was 14 when he was acknowledged and brought back to Lanling Jin Clan
23- 14 = 9.
wei wuxian was dead for 13 years before mo xuanyu revived him but he's in between 24-27 yo
14 + 13 = 27
lan wangji is in his 30s (22 + 13 = 35)
but 35 - 27 = is 8
so if he's just like wwx, then he must have some month gap with lwj
his age diff with wwx is 9 and with lwj is 8 but google says its 10
but it realy doesn't matter now because he gave his body up and wwx is now possesing it BUT. wwx died when he was 22, dead people don't age mentality so wwx is still 22 while lwj is 35