That's not what a gerontologist is.
He said it's "a medical practitioner specializing in anti-aging medicine." This is basically accurate. You could argue that one doesn't necessarily have to be a medical practitioner, but many different sources across the internet disagree on this point, so there doesn't appear to be a definitive consensus. "Medicine" in this context doesn't necessarily mean pills and drugs, but rather the scientific field as a whole.
On a completely unrelated note, on page 18, he shows that he's had the youngest vintage of wine on ice. My knowledge of wine is very limited, but I would have thought that was a gaffe, no? Don't people normally not chill wine?