It seems in every case among siblings, the younger sibling is superior to the older one, with the exception of Mako and Bolin. Could there be any reasoning?
Azula learns firebending much quicker than Zuko
Unalaq gets Tonraq banished and becomes chief
Ozai takes over Iroh's heir
Sokka is not a waterbender but his younger sister is
Tenizen gets more attention than his 2 older siblings
And quite recently...
Lin is the chief of police of a city while Su has her own city
Is there any influence in the Avatar world that causes this? Coincidence? Did having parents influence the younger to be superior but as Mako had no parents he became superior to Bolin?