https://www.dailymail.co.uk/tvshowbiz/article-12980061/Jodie-Foster-turned-role-Princess-Leia-Star-Wars-age-14.html
. . .
She was already contracted to do other films during
the period however.
IMHO, her more "brooding" personality would not have
been best for the film. Fisher was more irritable,
aggressive, action-oriented - stuff you might expect
from a "rebel leader" ... she was the better choice.
Being a bit older, it was also possible to weave
more "love interest" into the series. "Han" hitting
on a 15-year-old ... ok, it was the 70s ... but still
it may not have gone down so well. "Luke" hitting on
her ... that would have much complicated the later
bro-&-sis thing. And Foster ... well ... she may
have started hitting on some female character rather
than the boyz :-) By reports she was kinda AC/DC, but
soon enough settled on straight 'DC'
And now ... unbearably 'woke' ......... what a
waste of high IQ .........
For a continuing series, opposed to something like
the long-writ "Hobbit" films, the actors/personalities
chosen early WILL influence future writing.