The wording of the Bred for War trait is as follows:
Bred for War
You tower above most other humans and possess a physique of hard, corded muscle.
Benefit You gain a +1 trait bonus on Intimidate checks and a +1 trait bonus on your CMB because of your great size. You must be at least 6 feet tall. (Emphasis Mine)
Someone on the Pathfinder Society Facebook Group stated they have a Halfling who is 8 feet tall because they used the Adopted Social Trait to select it. I read the trait as requiring you to be six feet or taller to select the trait, not permitting an otherwise Small race to become taller than six feet via its selection.