"Go ahead already, gentlemen."
Translation:Gehen Sie schon voraus, meine Herren.
Is "already" being used in the colloquial, American English sense here? For example, saying "Go AHEAD already!", a command which suggests impatience with someone who has not yet done something? Does it have the same meaning in German, or does it mean something different? Or is it just one of Duolingo's strange constructions?
A few things, gentlemen when used to address someone should be translated as "meine Herren", otherwise it sounds wrong. Voraus gehen is to go ahead, what you wrote is wrong in that "odering" someone to go has to have a somewhere, but vorne is just location, not direction. You could say Gehen Sie schon nach vorne! Which would mean go to the front of whatever you are referring to.
"schon" means "already"
"mal" can be used for different things. It can stand for "einmal" (once). So "Gehen Sie mal voraus..." can mean "Go ahead for once..." Most often "mal" is simply a modal particle, so a filler, or used to intensify the meaning.
For a more colloquial sound, you can combine the two into "Gehen Sie schon mal voraus" which pretty much means the same as "Go ahead already"