Anyone over age 35 can become an Ambrosia customer, said Karmazin, but most of the early adopters tend to be of retirement age. He also stressed that it's a range of people, and not just Bay Area technologists, who have signed up.

About 100 people have signed up to receive an infusion, founder Dr. Jesse Karmazin said Wednesday at the Code Conference.

It might sound like science fiction, or a recent episode of "Silicon Valley ," but a start-up called Ambrosia is charging $8,000 for blood transfusions from young people.

The donated blood typically comes from teenagers, although anyone under age 25 is eligible. The company buys its supply from blood banks, which also sell blood to pharmaceutical companies. So high-schoolers donating their blood are not aware that it might be used on healthy adults.

Speaking to a roomful of technologists, Karmazin explained that the company does not claim that it can cure aging. Instead, he's hoping to recruit hundreds more people to research whether the transfusions can help fight particular symptoms associated with aging. Traditionally, biological aging hasn't been treated as a disease, which makes it challenging to study.

Karmazin said those who have signed up have seen some positive benefits and haven't reported any negative ones. Blood transfusions come with a variety of risks, including allergic reactions.

Karmazin started the company after reviewing research into whether injecting older mice with the plasma portion of young ones can improve memory. Other so-called parabiosis studies went a step further in connecting older and younger animals so that their blood mingles.

These studies are far from definitive, and scientists have spoken out about the ethics of such a study, which they see as taking advantage of the public's excitement and lacking much evidence. But the concept has seen a recent resurgence in interest because well-known Silicon Valley investors like Peter Thiel have spoken out about its promise.

But that does not mean Thiel gets teenage blood transfusions, said Karmazin, a graduate of Stanford Medical School. Karmazin stressed that Thiel is not an Ambrosia customer — and to his knowledge, Ambrosia is the only U.S. company on the market.

"Of course, it's possible he could have gone abroad," Karmazin shrugged. "But I haven't heard anything about that."

Thiel didn't immediately reply to a CNBC request for comment.