I'm a bit more flexible than UE in that regard, but I should warn you about the criteria we use for the characters' bio and personality. It doesn't have to be something incredibly outlandish (rather, if it is, it's gonna need some GOOD justification, and a nice talk with the GMs before accepting them), and it's perfectly fine to have a character that has some peculiar traits or skills, as well as a character who had a non-conventional life. But everything has to be consistent with the in-universe logic and common sense. For example, Yusei was an orphan adopted by a hostel in the Satellite, and he was a smart kid who joined a gang led by an older, much more "direct" guy. He's not led exactly a comfortable or uneventful life, at least by current Western middle-class standards. And is the only character who didn't go to an actual prestigious school, because of that. He had no reason to, after all: Martha and Kalin pretty much taught him everything he could need. He has his own personality, which is consistent with his actions and backstory, which is detailed by key events.
If you want to write a backstory, you should pinpoint some defining events and characteristics that will make your character memorable - and explain how he got where he did. It's a bit unlikely that a boy from an impoverished family just decided to join Duel Academy. Give us a specific reason as to why and how. For example, he could have met a professor from the academy who liked his duelling style and suggested him to go to the Academy, he felt, after some soul-searching, that learning to duel and maybe getting some much-needed high-school education would actually help him support his family, and worked hard to gather the money to pay for his studies at DA.
Not much of a change from the bio you wrote, but doesn't it feel much more real? Remember: as, like you said, it's pretty much impossible to write something absolutely original (not that YGO was all that keen on that, even :P ), the difference is in HOW you put it. Then yes, maybe it's been done before. But if you tell it in a more believable way, it gets pleasant to read nevertheless.

Try to reflect on this advice. It's been given to me, when the time was right, by a true writer, and well... it's done wonders for me so far.