Hyperbaric chambers don't have any claimed potential to reverse aging IIRC. What they do is increase 02 levels, which increases metabolic rate. This actually would accelerate aging since that is a result of using the metabolic processes to live, as I understand the aging mechanism.

However, restoring the presence of the blood markers of youth indeed retards aging, which is characterized by decreasing collagen, which makes skin less elastic causing wrinkles, for example, but across many and diverse suites of factors that enable younger individuals to heal, grow, and perform faster and better than the aged. I am as certain Thiel uses young blood as I am that the sun will rise in the morning.