You're looking at the wrong angle. You're only considering a story that has character development as one of its key dynamics, instead of the plot around the main character. Which granted was there. But you don't always have to have huge changes in your character as the plot evolves. Part of an RPG is the adventure. If Auron or Lulu lead, most of what happened would have still happened. They followed the religious thing, and then rebelled against it. A teenage love story wasn't necissary to develop the plot.

Besides. Characters can change at any age, as was stated. The only example you're considering is a change in maturation. But people can change their point of view too. Wakka didn't grow up, but his character developed too. His wasn't a coming of age story. It was him casting off his ignorance and bias racism. He was an older character