When my late wife asked our 90 year old neighbor what the secret to her longevity was, we got a shocking answer, “I tried never to do anything to help other people, and only did things for myself” was her answer. Needless to say, it was something of a shock to hear her say that her long life was due to her selfishness.
Funny, 8 years later, she is still alive, but my wife has been dead for 4 years, and died at 39.
Maybe she is on to something.
Wrong metric. It’s not the length of a person’s life, but the quality of the life they lead.
But I think your neighbor is wrong. I think a certain self-interest is a good thing like having healthy boundaries. But there is much to be gained from helping others and IMO that gratification is good for the mind and in turn the health of the body. I'm afraid no one can see or foresee all of the tremendous number of variables that come to play in our lives though.