Longest RP I have been part of, [url=http://www.roleplayerguild.com/topics/19063-precipice-of-war-we-write-under-the-sign-of-the-goat/ooc]and still am[/url], is right now clocked at [url=http://forum.spore.com/jforum/posts/list/68292.page]4 years and 7 months old[/url]. There was only a short gap back in 2011 when it was dead for four months, otherwise it trudges on. We move slower now, and a lot of that is the loss of people, but some of that too is from those of use who are still with it making longer, more detailed posts now. 

I think it helps that quite of few of us were already adults and already had schedules when the RP started.