Here's a fantastic story about the current state of Charter school athletics. Good for them, I say. DCPS has failed them for decades now.
http://www.grantland.com/story/_/id/7710473/aazaar-abdul-rahim-rise-new-washington-dc-football-power-friendship-collegiate-academy
And the 5th year eligibility thing is something that Michelle Rhee implemented for DCPS schools a few years back so it's completely understandable that charters could have followed suit...it's pretty hard to follow the willy nilly changes made by DCPS. Read up on the history.
http://www.washingtoncitypaper.com/articles/34679/welcome-13th-graders
http://www.washingtoncitypaper.com/blogs/citydesk/2010/01/22/cheap-seats-daily-michelle-rhees-ok-with-redshirting-athletes-again/