Sick and tired...

Ugh not 4 year old son won't stop copying his older sister!!!! It used to be cute but now it's just like "dude be your own person!" She will come home from school saying she did something there and he will say he did it too. I can't get him to understand that when he says he did something that he didn't it's a lie. I was hoping when his sister started school last year he would become more of his own person but it just seems to get worse. Everything she does he wants to do. Right now he is throwing a tantrum cause he wants to read a book like she is but he didn't ask if he could. Any advice on getting him to stop copying her???