When R. Yochanan heard that there are old people in Bavel, he was amazed, for it says, “Lema’an Yirbu Yemeichem vi’Yemei Veneichem Al ha’Adamah…” — long life is only in Eretz Yisrael!
Didn’t R’ Yochanan know that outside of Eretz Yisroel there are even old Gentiles? That there are also old animals and ancient trees? It is not that unusual that one is “amazed” by such an occurrence! Besides, these Gentiles, animals or trees don’t need a special zchus to grow old naturally! If so, why should a Yid be the ONLY species that needs a special zchus to reach a “natural” old age??