My wife and I raise (and eat) dual purpose birds, mainly Delawares. We process them right at 3 months. This means smaller birds compared to grocery stores and what many of you do, but the 1 3/4 to 2 1/2 lb birds are sufficient for us to have 2 full meals from.
More importantly, that is the ideal age for our birds to have both the size and tenderness we expect! We brine them in salted ice water at processing to get all the blood out, then we age them in the fridge for 4 days before cooking or freezing. We often stagger batches so we don't have too many in the fridge at one time. I have been eyeing one of those mini (dorm sized) fridges just for aging meat or cheese. Heck, maybe I should just get a full sized one for when I process sheep when the weather is warm!
Anyway, the chickens are tender enough to be cooked with any method we want, and so flavorfull! Uh...I think I know what I want for dinner!!!
~S