Question: If Amazons are immortal and never age then how can Diana grow up there?
Answer: It would be more accurate to say they grow to a certain age then stop aging. Similar to the elves in Tolkien's Lord of the Rings.
Answer: They may never grow old, but they are not immortal since we see some die.
Answer: Diana is unlike the other Amazon women, so her physiology differs. In mythology, Amazon women were demigods - half human and half god. Diana's mother, Hippolyta, crafted her from clay and Zeus gave her life. Diana grew from an infant into adulthood, then, like the other Amazons, becomes either immortal or long-lived.
Answer: Thank you both.
Question: Why not tell her the truth? She wouldn't have been worse off. If he'd wanted to find them he could've done so sooner.
Answer: For the majority of the movie, Diana believes the sword to be the only weapon capable of killing Ares. She doesn't realise until she fights him that the sword is just an ordinary weapon and thus, useless against a god. She carries the shield because it is useful. She uses it in combat most prominently to block gunfire.
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