I have wanted to become a manager ever since I was ten years old,这句话有错吗？

可以的。还不错哟！！

可以改为 Since I was ten years old,I was longing to become a manager.

没错啊……

have+动词的过去分词 表示现在完成时
但是从句意上讲，你的想成为经理人或管理者的愿望还没结，可能还在继续要用现在完成进行时