[@Tatsua Aiisen] You shouldn't be worried about starting a debate, otherwise we'd be stuck wondering 'what is dis?' and twiddle our thumbs until nothing happens, that being said . . .

I agree and disagree with you. From what I've seen, the Patronus is a relatively simple spell to learn circa sixth year. From what I've read, the Harry Potter world is heavily dependent on innate talent for casting magic. Who teaches you what actually plays little part in casting the more advanced spells. Honestly, Harry learned it in his third year while the others learned it in their fifth year; irregardless of the circumstances, a sixth year learning about it shouldn't be too unusual - impressive, yes, but not unusual - as they're one year close to graduation. 

As for [i]why[/i] and [i]how[/i] they learned it, that is entirely up to the person playing. I just want to point out that it's not impossible or unusual for a sixth year to learn said spell.

[sub]Also I have to laugh at Dumbledore's Army being called 'elite' - that's one gross overstatement, and Harry himself was not exactly a prodigy with magic. Talented, yes, but overall not very impressive; his magical talent was based on his dueling skills and reflexes rather than any actual genius in spell casting.[/sub]