The Secret Life Of Walter Mitty, even though a bit slow and awkward in the beginning, came out to be a somewhat engaging story with BEAUTIFUL scenery and videography.
Why iffy for age 11? Well to start off, sadly, although PG some language was put in that was not necessary. S--t once, A-- once, H--l a few times, D--k once. And, also some crude remarks having to do with sensuality.
Violence, although nothing major, there is a brief shark attack scene (no one is hurt) which may scare kids.
Besides that, i would say it would be a fine movie for +12. Younger tweens would want to watch with parents.