I am physically weak!!

I am 17 years old. But I face problem in carrying 20 Litres water bottle jar 200 m on my shoulder. My brother is 2.5 years younger than me but he easily lifts and carries out. He always beats me down in arm wrestling. Literally everybody beats me down in arm wrestling. He hasn't done any kind of workout. Still. Should I join gym because I am in a serious condition?