Which is all arguably better, in that you don't get elderly protagonists all the time.

This is very true -- the fact that two of the most important characters in the movie were old men means something, but clearly doesn't help in regards to girl characters.

Now I'm wondering...what might the movie have been like if the gender roles were reversed? If Carl was more the adventurer when they were young, Ellie the meeker one then -- but grew and learned to be brave and adventurous when she was older, after Carl passed away? The fundamental message of the movie could've been the same, and I think she could have bonded with Russell just as easily...