Thanks so much Teacher 8! I have another question then

If the I-130 takes 4-5 years, so the whole process will take 4+12=16 years for F4 category? or the total is about 12 years including the I-130's 4-5 years? what date is the priority date? the date I submit I-130 or I-130 get approved (my understanding is this one)? I understand only when Priority date is current, then the applicant can submit I-485. So how to calculate CSPA age? is that the time when I-130 get approved? or the time to submit I-485? is the freezing age protection covering this F4 catagery (sister's son) or just only for citizen/GC's child?

Thank you again for your help!