This is a gift link. It does not specifically mention rapamycin, but does discuss “immune youth” in older folks as being associated with higher rates of autoimmune disease.
"Scientists continue to look for new ways to keep the immune system strong to help older adults fight infections and cancer. But some evidence suggests having the immune system age in tandem with the body could have benefits. More than 100 older patients in their 60s and 70s treated at Mayo for an autoimmune disease that attacks the arteries had unusually vigorous immune systems that had not slowed with age, dubbed “immune youth.” But instead of protecting them, according to a study, their youthful immune systems attacked their normally aging tissues as if they were foreign invaders.
Without the means to rejuvenate the entire body, warns Dr. Cornelia Weyand, director of Mayo’s program in immunity and inflammation and co-author of the study, “rejuvenating the immune system alone creates the risk of autoimmune disease.”"