I can't find the dual option on iOS
In the screenshots of the app there is an option to dual at the bottom of the page... I ain't got that?! Just a big blue bar that says practice weak skills. Do I have to unlock duals or am I missing something?
I think he has the latest version (I have the same exact version [according to what he's describing] of the Duolingo app, one blue button at the bottom saying "Practice Weak Skills", no dueling feature) of Duolingo. I would post a screenshot of my profile to show you, but can't right now.
EDIT: Found a picture of the version he's describing (slightly different, though): http://i.imgur.com/0aWDrQl
Unfortunately, you can't unlock duels. I have the exact same version as you do (there's a big blue button at the bottom that says "Practice Weak Skills", and no option to duel) and I think there's absolutely no way to unlock or get to the dueling feature. Sorry! :(
But, you can make another account for duels (some accounts have different layouts)... but first you're going to have to do a few lessons before the feature becomes available.