Idk about *THE* oldest. I was "into" guro and related violence themes since 2007-2008 (ish...), basically not long after I started to have interest in sexy stuff in general in my teen years as puberty hit. But my hard drive died in early 2009 so I definitely lost some of the earliest content I had stored.

Here's some stuff that is dated to early 2010 in my folders that I can still find easily: