My mom was petitioned by her sister with a priority date Feb. 1987, it is a family status meaning including my dad and me, then after 23 years the notice came stating that we have to assign an agent and pay the affidavit of support w/c is $70, then when the notice to pay $400 came, the only names appeared are my mom (the principal/ sister of the petitioner) and dad's name only, does that mean I'm no longer eligible as their dependent since I am already 27 yrs old but still single and by the way I'm an only child, please help me figure out what moves I have to take, thanks so much, I will surely appreciate a reply

You are excluded because you're over 21. In this case, wait until your parents become permanent residents, they can file a petition for you but it will take several years.

Thanks for the reply, but may I ask also approximately how long will it take if my parents file a petition for me?

Depends on where you're from... what country?