Sorry Zoro, You Don't Meet The 'Qualifications'
It kind of saddens me that members here (new and old) are actually getting worked up with the whole "Zoro being the First Mate" thing.
To make things clear, Zoro was never officially titled the First Mate of the Straw Hat Crew.
In Chapter 499 p.16, Urouge refers to Zoro as the First Mate but this seems to be a scanlation/translation issue as the RAW did not use first mate, it used 副船長, Fuku Senchō, which is generally translated as "second in command"…which technically IS the First Mate anyway...
Whatever the case is he isn't "official".
Now imo, I think it is obvious he is the first mate with or without it being said. Yes you can google "First Mate" and it will give you a job description that really is kinda irrelevant to the OP World because if Oda see's Zoro fit to be the first mate despite him not meeting even half of the "qualifications" listed on www.ICantThinkForMyself.com/search/Real_World_Job_Description_Of_A_First_Mate/ then so be it….and everyone would not have an issue with it anyway.
With all that being said, don't you think Oda realizes this? I wouldn't be surprised if Oda decided to bring out the official labels fairly soon as things are getting a lot more serious, the big shots and feared are in the world that Luffy is heading straight into and his crew wouldn't look…organized...or official (despite there reputation) without properly labeling each crew member like most (if not all) of the crews we have encountered. If WB's crew and Rogers Crew had an extensive ranking system...don't you think the future crew of the Pirate King would have some type of ranks in the least by the end of the series?