under 21, petition made by the mother (resident)
The NVC doesn't "approve" it. It is already approved by USCIS when it is sent to the NVC and they hold it until a visa is available. There are different waits depending on what country you are from. You have to wait until your priority date which is usually the date your I-130 was approved. You can check the visa bulletin for thd priority date they are currently processing. You will be in category family 2A. Currently the wait is about 4 years and 5 if you are from Mexico. If your mom Naturalizes you can move into F1 category which is a few years shorter.
If you get married before your mom Naturalizes you will lose your priority date and have to start over.
Current Visa Bulletin-
You may call me for a free consultation at 206-724-1940.
Andre Olivie, Esq.