If you just do t want them and dont plan to process them, then sell them now. You could process as young as 6 weeks for a decent bird, but 7-8 weeks should get you a good supermarket size bird.
if you process before sale, that will depend on your location. What state are you in? I’m in Ohio and I can sell processed chickens from my “doorstep” to an individual, up to a certain number per year. But, not all states are like that. Selling any other way (like to a restaurant) takes a lot more requirements. Some states do not allow you to sell at all without certain requirements met.