any bird can be just about any age. However only cornish cross will give a 5 pound dressed bird in 8 weeks
freedom rangers take 10-12 weeks or more depending on which post you believe or feed you offer.
6-8 is cornish cross only unless you are looking for a very small dressed bird
Cornish x is very specialized I don't think any of the backyards have them. Some are experimenting with keeping and hatching .
You might get a bite with the freedom ranger.