While they are released from their AS oaths they are required to take Oaths to the DO. Its not the fact that the oaths are the Aes Sedai oaths that give them the ageless look its the oaths in general.
The only real difference between the Kin and Aes Sedai are the oaths. So its pretty fair to say the agelessness is caused by taking the Oaths on the Oath rod. As the old Aes Sedai did not swear on the Oath Rods and as you can see the Chosen also do not have the agelessness.