Often times when a school or gym brings in a guest instructor, it is someone much older than the students and/or the regular instructors who has a wealth of experience and has probably forgotten more things about what they are going to teach than the students and/or regular instructors could ever hope to know.
However, in the case of Team Lloyd Irvin of Camp Springs, a school known for producing mixed martial artists who compete at the amateur and national level, they brought in a guest instructor who would probably me among the younger students.
The school recently hosted a Brazilian jiu-jitsu seminar by J.T. "Spiderman" Torres, a world-renowned BJJ competitor who is all of 19 years old. But despite his age, a YouTube video is posted on the above link with Torres giving another seminar at another gym where he seems to demonstrate the expertise and savvy that would probably rival some of the foremost minds in the art of BJJ.
Torres has apparently made his name against some of the other young stars in MMA in various BJJ contests. Here's a video of Torres submitting UFC welterweight Dustin Hazelett in less than a minute.