Re: The plan...
Interesting article about blood. Blood doping* has been around for years in athletics: Lasse Viren allegedly used it when he won Olympic gold medals in the 5,000m and 10,000m, at the 1972 and 1976 Olympics, but it is now illegal in sport.
(There is also altitude training, but that is legal, and has its own disadvantages. The England (association) football team tried it at one World Cup, but got it wrong, and were very lethargic in one crucial match. At altitude you blood thickens, so when you return to sea-level you need a few days for your blood to regain its fluidity for the greatest health benefits.)
If you want blood transfusions from young people, I wonder whether you can freeze your own teenage blood, and get it back safely in middle age. (Much too late for me, sadly, but some of you could still save yourselves!)
Basically, tinkering with you blood can be tricky.
https://en.wikipedia.org/wiki/Lasse_Virén
*an athlete gives blood which is then frozen. The athlete trains, recoups the lost blood, and then, just before a major sporting event, such as the Olympics, the donated blood is re-introduced, so the athlete is somewhat over-supplied with blood, which gives them an advantage in aerobic competitions such as long distance running or long cycle races. Thera are dangers as excess blood can be problematic, even if it is your own.