不符合语法,正确的说法：
I was only seven years old when I did housework for the first time .

祝你开心.I had done some housework for the first time when I was only 7 years old.这个行么这样也可以。理解为：“我做家务”发生在“我七岁”之前，即“过去的过去”，用过去完成时。