How old is this boy?

Hyomyung Shin looks like a healthy child. But what you can’t tell by looking at him: He was born in 1989. He is 26 years old— but he’s still waiting for the onset of puberty. The South Korean man suffers from a very rare genetic condition called Highlander Syndrome. Only a handful of cases have ever been recorded. Those affected age extremely slowly— or not at all. Will Shin live far longer than the average human? No one knows, because Highlander Syndrome is uncharted medical territory. But the answer to one of humanity’s oldest questions might be contained within Shin’s DNA: Could this as-yet-undiscovered key help us put the brakes on aging?