Why is my younger sister stronger then me?

So it looks like this.
Why is my younger sister stronger then me?


There was a huge water package and I couldn't physically carry it no matter how hard I tried while my younger sister who's 9. Could carry it with no issue at all and I don't understand why can she carry it and I can't? She's 9 and I'm 16 why couldn't I carry it? I'm 130 pounds is that fat?
Why is my younger sister stronger then me?
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