Board Thread:Speculation House/@comment-85.130.101.225-20130816112245/@comment-3146930-20140722214052

For me Aura doesn't have to be unlocked by someone, but can be unlocked given enough time and training. With Jaune, Pyrrha basically had to unlock it or else Jaune probably would have died in the forest. If he had gone to a combat school like everyone else had and not cheated the system, then he too would have had his Aura to protect him and maybe even control it. Ren for example probably has great control of his Aura because that is what he trained himself in or someone trained him (like a family technique passed down to him or something).

There is also the possibility that like you said, unlocking Aura without any kind of training could be dangerous to the user or those around him (food is forced away from their mouth by Aura). It may also be constantly active, as Cardin and Jaune's Auras were being measured during a fight, so even if Jaune can't control it his Aura is still there. Then later after taking a beating from Cardin and then the Ursa Major, his Aura levels are still displayed so it was giving him at least some protection during the fight.