>>1069476>>1071818>>1071922If the new series starts 75 years after the war and Korra is 16, then Aang died 59 years after the war at age 72. Assuming Tenzin was born when Aang was 18, he would be 53.
The thing that bothers me about that time frame is Korra. In the third season, Roku said the avatar wasn't revealed until he or she turned 16 and it took years to master the elements. Also, learning the opposite of their natural element (in Roku's case waterbending) was extra hard. It doesn't seem likely Korra would have mastered earth and fire that soon.
Maybe she was revealed early like in Aang's case? Part of her story could involve not having a normal childhood and stress from the responsibility of being the avatar.