Side note! They ish 20(Ish) and Iam 40 >_> POssibly looking to Team to null the level gap then Duel.
There is no /duel feature in the game.
However, you can either go to a PvP zone (only Warburg is going to let a hero fight a hero, though, and that's too high of a level for you), or go to the Arena, and set up a fight there. The Arena is likely your best bet, and they can be found in several zones around the City.
Let me never fall into the vulgar mistake of dreaming that I am persecuted whenever I am contradicted.
~Ralph Waldo Emerson
"I was just the one with the most unsolicited sombrero." - Traegus
Actually, you can now start an arena match no matter where you are.
They added an Arena option to the Menu in I17. Just pick that option and create an event to your liking, then invite your buddy to it and voila, you can beat each other up.
As for levels, I know that you can exemplar down to his level, meaning that you'll be combat level 20 and have whatever powers you picked up to level 24. There might be a way to have him sidekick up to your level, but I am not entirely certain that is possible.
A little reminder, powers behave a little bit differently in PvP than in PvE. Different damages, lengths of duration, and effectiveness. Some are higher, some are lower, etc.
Me and my buddy wanna duel each other (Both heroes) See who is better <_< How can this be done? Can it be done?