Flynn's father, Carlo, served on the crews of a number of different merchant vessels throughout his life. In 902, he was one of the officers of the Woodsorrel, when the first mate retired, and was replaced by Alphonse. Al would become friendly with a number of his new crew mates, including Carlo. The bond among the entire crew was strengthened the following year, when they served together in the Protestant navy. Sometime after the war, the captain of the Woodsorrel retired, passing on command of the ship to Al. (Though many among the crew had served on the ship much longer than Al, he had been a sailor more years than most of them, in spite of a long stretch of time during which he had worked as a history master rather than a sailor. Besides which, the crew had plenty of chances to witness Al's skill and intellect during his time as first mate, so no one objected to his promotion.)
When the surname law was passed in 904, Carlo chose the name "Sharpblunt," though neither he nor anyone in his family seem to recall just why he chose that name. Flynn himself has said he vaguely recalls his father explaining it to him, at the time, but he doesn't even remember whether he liked the story his father told, or not. Nevertheless, Flynn has always thought it was a cool name, and says the meaning behind it is unimportant.
After Al became captain, he renamed the ship Woodsorrow, and took a vote: he wanted to turn to a life of piracy, but he didn't want to do that unless the majority of the crew agreed. Because of all they'd gone through in the war, and perhaps for political reasons as well, most of them had no desire to just go on with their lives and accept the changes the Second Order was making to the world, so they chose piracy as a symbolic act of defiance, even if it did nothing to hurt the new government (and certainly they always avoided the navy, knowing they'd be outmatched). But a few members of the crew chose to leave Woodsorrow, including Carlo. After all, he had a young son to raise, and didn't believe it would be fair to Flynn to constantly risk death or imprisonment, thus leaving him fatherless. So, he found work on a different merchant vessel. He might not be at home as often as he'd like, but at least he'd be a better father than a pirate.
However, he had always taught Flynn all he knew about sailing, and continued to do so after the war. At age 16, Flynn decided he wanted to become a pirate. And in spite of the fact that his father had thought it best that he himself not be a pirate, he remained friends with his old crew, including Alphonse, who over the years became like an uncle to Flynn. This made it a simple matter for Flynn to get an entry level job on the Woodsorrow in 908, and he worked hard to prove his value to the crew. Three years later, when the first mate retired, Flynn was granted the position, at merely 19 years of age. While some of the crew may have found the promotion questionable, none of them complained, as they knew quite well that he was at least as good a sailor as any of them, and probably smarter, given the love of reading that he shared with the captain. It was around that time that Cara MakeDo joined the crew, and the way she worked hard to prove herself to the crew, in spite of her young age, reminded Flynn very much of himself, a few years ago. So he began pushing her even harder, to achieve her full potential. They soon became friends, and she credited him with being a big help in her becoming a junior officer, after less than a year on the crew.
In 912, just a year after becoming first mate, Alphonse was approached by Cara's cousin, Darius Lonewander, who was organizing a rebellion called The Chaos, and wanted Teach to see if he could assemble various pirate crews into a navy for that rebellion. Later that year, those ships Al had gotten to join served Lonewander in the Chaos War. The next year, when the United Villages of the Chaos was founded, Captain Teach became Admiral of the Chaos Navy, and Flynn rose to the position of captain of the Woodsorrow.