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我不确定approval date是否就是notice date还是receipt date，
-The approval date is the notice date on the approval notice. Receipt date is the I-130 filing date (i.e. the priority date).

我的实际年龄已经超过21周岁了，但是当时缴费时已经交了我的那一份，而且今天收到的email， case里也提及了我的名字和信息。
-Then, it seems you may have no age-out problem. So, you may just go to China to apply for the immigration visa together with your mother because you have paid the fee. If you get the immigration visa in China, you have to either come to US together with your mother or your mother enters US first using immigration visa, and then you enters US later. You can not enter US before your mother enters US.