No,it is not hormones. It is simply a matter of a combination of genetics as well as a lack of toning. All women have genetic predisposition towards the shape they will take as they age and when hormonal imbalanced. if you do not resist this shape during times of increasing or decreasing weight i.e pregnancy, menopause, extreme sports,etc then you will take the shape you were destined to be. That is why toning is incredibly important. Women always require toning exercises to be a certain shape, losing weight simply with dieting or doing cardio results in fat loss but no muscle tone and gives you flaps of skin and a poor shape. In order to change your problem with your arms you will need to do weight training with weights of above 4kg or more (the heavier the weight the quicker the result).