I mentioned telomeres - which is what I think he was referring to. These are not genetic markers or part of the genetic code, though. They're attached to the end of your DNA strands and keep the DNA from "unwinding".
On a slightly unrelated note, but on the topic of genetic modification, there's a gene that can be activated in your cells that allows telomeres to regenerate after a cell divides. As I understand it, though, while in theory it would make you live a lot longer, activating it also prevents cancerous cells, which reproduce very rapidly, from dying off like they typically do. Apparently miniature tumors can appear on body at various times, but die off quickly because the gene that allows the telomeres to regenerate isn't active. Activating that gene would make all of these tumors turn into cancer, which last I heard was the major obstacle to research into this method of increasing longevity -- but that was almost 7 years ago, when I was a freshman in high school.
Incidentally, the speaker that talked about this (among other topics) said that the treatement, along with a myriad of other things, would be available in about 5 years. I guess the research hasn't gone quite as well as they had hoped.