I just had to rehome three accidental roosters. Be aware Facebook I don't think allows selling animals, so I had to find a local chicken page. While my local Facebook chicken page is very active, a lot of the posts made me concerned about care. Basically social media nutters denying science based chicken health issues and touting "miracle supplements". While I needed to rehome my roosters asap, it was my last choice. Hopefully your local Facebook page is better. I found neighbors on NextDoor (localized social media basically, same Fb flaws, but local), but it took me a few weeks. I felt fortunate that both were homes that sounded great (I've even had an update photo from the family that needed a new roo, and the other two went to a home of a man excited to start breeding pretty color laying chickens for his extended family), but I admit I took advice from here on BYC that do the best you can rehoming, but then accept they aren't your chickens anymore.
As to their age, my two five-year-old hens are laying three eggs every two days, so it depends on the bird. To me, three year old grown hens would be welcome in my flock if I had more space. It's basically a starter flock, already laying. Just warn their new family they may stop laying until they are comfortable in their new home.
