Not a doctor, but a PhD with some work on protein pharmacokinetics. Serum albumin and antibodies are the two longest lived proteins in your blood because we have special mechanisms and proteins to salvage them from where other proteins get degraded. That’s why their half life in blood is in months. They’re also (unless you make them targeted) benign in many ways (hence IVIG is used fairly indiscriminately). Thus, of all the longevity related therapy ideas, this seems the most benign. And makes a little bit of sense too, though further mechanism studies are needed (which are always hard).

If Peter Thiel or some other longevity obsessed techidiot is reading this though, don’t go around injecting albumin into yourself yet - and don’t talk to quack doctors obsessed with longevity either. What I’ve learned time and again is you always think Ying and your body’s biology will come and Yang you in the kidney.