A study with sample size 1 is called a 'Case Study' and is used all the time in various hard sciences.
Larger scale studies are of course stronger. But case studies have depth and are often the source of good hypothesis or the inspiration of other tests.
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That being said, this dude looks like a quack to me. But the alchemists we're all quacks but still laid the foundation of modern chemistry. So it ended up all being worthwhile.
This isn't a case study. He is self reporting. With the amount of measurements he takes on himself he is bound to find something "statistically significant" by chance. p=.05 is still a 1 in 20 it's bullshit. Measure 20 variables and you'll probably find something "significant" just by chance.
This dude should be called out not for being a quack or for wasting so much money. He should be called out for using his son in this way. Hundreds of thousands of Americans need plasma transfusions every year. He's doing it for fun. And objectifying his son in the process.
There's a lot of exciting science happening in the anti-aging field. There's a reason researchers in the field think this is not only pointless but reckless. I've been hematoma'd. It's not fun. I would never speak to my father again if I got a hematoma or some other complication because he's afraid of his own mortality.
Larger scale studies are of course stronger. But case studies have depth and are often the source of good hypothesis or the inspiration of other tests.
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That being said, this dude looks like a quack to me. But the alchemists we're all quacks but still laid the foundation of modern chemistry. So it ended up all being worthwhile.