I did it in my book ECHOES OF A SILENT RIVER ( Booklocker.com)
In fact BOTH main characters were male..and this was at the time of the Civil War to boot.
I think it takes an *ear* to SOUND like a man...and I know some may think that this sounds sexist..but trying to get inside the HEAD of a man may mean ( at least for me( that the male character is more *visually* oriented.
By that, and this is a cliche..but they say men speak when they have something to say...women speak to find out what they THINK.
I think that is why if male characters are doing a whole lot of emoting, touchy feely stuff, yakking a mile a minute..they often come off in PRINT as if they aren't quite manly enough.
Unless that is the way your Characters are of course.
Just being observant of how guys that age relate is prime, how do they walk? talk? What ethnic group? Background? Geek or Jock? Average Joe or Prep school grad? The CHARACTER will determine who you will be looking at to do *research*
Maybe you could do a section of dialogue...show it to a few 20 year old guys. Not to critique it extensively, but to just see if it seems AUTHENTIC for a 20 year old guy in that group
My friend who does childrens stories ALWAYS...ALWAYS..ALWAYS makes sure the stories she writes are read for *fun* to kids that AGE in a casual atmosphere. She TELLS the story to kids that age.
THAT way just by being observant...seeing if they are bored with one part, excited with one part, booing or hissing at one part...she gets a feel for whats *real* and what might need tweaked.
The Risky Writer http://theriskywriter.com
Because NO Good writer plays it safe!