Most elite throwers prefer a larger diameter shot because there is more surface to push against. Other throwers like a smaller diameter shot because they can control it better or may have smaller hands. Above all, choose a shot that feels comfortable to the thrower.
Women from High School thru age 49: 4.0 kg. Women age 50+: 3.0 kg.; Women age 75+: 2.0 kg. High School Boys: 12 lbs. Men to age 49: 16 lbs.; 50-59: 6.0 kg.; 60-69: 5.0 kg; 70-79: 4.0 kg.; 80+; 3.0 kg.