Mother initiating son in a female dominant world

[philadelph]

Hi, I am looking for a sci-fi/incest story I found on here a few years ago.
I remember it being centred around a mother and her son and the initiation ritual that boys in this future world go through on their on 18th birthday. He was *very* submissive, and the story went heavy on the pegging. The ending was her coming back into his room later that same night, and him willingly opening his legs for her. But I don't remember the title or their names... does anyone know this story?

 

[red_sky_cloud]

Probably something from theredheadboy.

 

[philadelph]

that was it.. thank you