over 21 year old son of a person with retained rights

Hi,

I just turned 21 Yesterday on 19th February 2017. I just needed to couple of questions regarding my situation.

Me and my mother moved to uk on June 2012 on the basis of my step dad being EEA national after getting a family permit. After arriving in uk we applied and received the residence card on February 2013. After that my step dad separated and divorced was finalised in December 2015. My mother sent the retained rights of residence application in May 2016 and we both received new residence cards valid for another 5 years.

No my question is that before the 5 years permanent residence qualifying time I have now turned over 21 yesterday. with still about one year to go for us to apply for permanent residence. Now the regulation states that family members can also be direct descendants who are dependant. My issue is that I currently work full time and earn about £1100 per month I'm also doing an IT course. My mom also works part time but earns only about £450. We share both our incomes so there is no actual bank transfers from my mothers account to mine etc.

To be eligible for permanent residence should i Quit my job so that i can prove i'm dependant family member ?

And if i do will i only need to show it for the period after i turned over 21 ?

Is there any other way I can move forward to this ?

Timeline:

Moved to uk on family permit June 2012
Received Residence card on Feb 2013
Received retained rights of residence Nov 2016 (Received new residence card both me and my mother)
Turned 21 on 19 Feb 2016
Need to apply for PR by Feb 2017

Any information will be greatly appreciated.

thanks