Do we really believe that Bevin never got held back? My assumption was that she repeated at least one grade in highschool, which could explain how she would know Quinn, Taylor, and Haley. (Also a lot of "high schools" have jr. high students from 7th-12th in one building. So they could have gone to school together if Bevin/Haley were in 7th grade and Quinn was a junior or senior.)
Actually, there was never any indication that Bevin wasn't book smart. Remember in 413 - her talk with Rachel...
"I know people think I'm stupid but I'm not dumb. I just let you and the other girls have your way because that's how you need it to be. But I think Carl's right. Pretty soon we're all gonna graduate and I can start over. It'll be harder for the people who need this place to make themselves feel special. People who use high school to build themselves up and then find out that the real world doesn't care so much about who you were in high school. People like you."
While it was clear that Bevin was ditzy, she also pretended a lot as well and it didn't mean she was academically stupid. Ditzy and stupid are not the same thing.
In terms of the James sister sequence...
The James family was always one of the continuity errors on One Tree Hill. I mean, Haley talked about being born into a big family with sisters AND brothers. Vivian was actually mentioned by Nathan in 211 yet once season 7 came, she was seemingly forgotten about along with all of those so-called brothers. So I've come to just accept Taylor, Quinn, and Haley as the only James siblings.
Please don't do the "longtime fans vs newbies" stuff. I happily admit that I am a newbie to the show but that doesn't mean I automatically know less. That is quite a general and quite frankly, insulting statement. As long as one has seen and/or has the ability to go and search through the episodes, anyone (even people who aren't fans of the show) can "answer" that question. Since Quinn's age or her place in the James sister line-up has NEVER been mentioned on the show then it's anyone's guess and opinion on what that answer is.
However, there are more refererences to insinuate that she is in fact younger than Taylor. Here are some examples:
1) Quinn could have easily been a junior when Taylor was a senior/Haley was a freshman.
^^^The show began at Haley's junior year so both Taylor and Quinn would have been graduated from THHS, hence explaining their absence at the school or at the James residance.
2) Quinn made this comment in 708:
"When Hales was in high school, she used to get all stressed about grades and tests and we would make special brownies."
^^^One could assume that this began Haley's freshman year (Taylor's senior and Quinn's junior, carrying into Haley's sophomore and Quinn's senior).
3) In 709 (I think that was the episode), Quinn told Clay that she and Haley used to volunteer/read (whatever that was) together in high school.
^^^Again, that could have been the Haley freshman/sophomore and Quinn junior/senior years.
So with these references alone plus the online source (no matter how reliable/unreliable it may be), I choose to believe that it goes Taylor, Quinn, and Haley. And for the record, I've always assumed Quinn was younger than Taylor since season 7 and I never once looked at anything online. I have never looked up anything on Wikipedia. This is just my perception of it and that's good enough for me since there is more evidence to support that theory - not to mention, there is no right answer here since it was never said outright.
And I'm sorry but what is that picture supposed to prove? For one thing, how do you know which girl is who? That picture is fan-made; a fan inserted those names. Who's to say he or she was right? There was never an episode where anyone pulled that picture (or any others) out and pinpointed who was who. So that picture is as reliable/unreliable as Wikipedia may or may not be. And secondly, let's say those names did in fact fit correctly with the girls - that still doesn't give an age away. Those girls all look relatively close together in age and it's not like they have distinct genetic features to prove anything. Even a girl (or boy) who is smaller than another girl (or boy) may in fact be the older one. Heigh, weight - that's not completely affirmative when finding a relative age.