there are really no chickens that will remain tender as they age. the longer a chicken lives, the larger and heavier it will get, which means it will have to get stronger to support its own weight, which in turn makes the meat tougher, and the longer a chicken lives, the more it moves over the course of its life, which makes the meat tougher. pretty much any chicken over about 9 months old is going to be some degree of tough.
with a meat bird, you're going to end up with a bigger meal than you will with almost any dual purpose chicken. so the trade off is sort of tenderness/size in exchange for flavor.
you have a few options: you can try to confine the meat birds that you get to limit their activity level which might buy you a few more weeks. keep in mind it may also might result in the loss of birds due to fighting in close quarters. plus, disease would need to be considered. i can honestly say that i know nothing about that particular approach personally.
or you can learn to work with an older chicken. there are some ways to manipulate the chicken once its been processed. for starters, you can hang it in a meat fridge for a week or two. hanging it is going to stretch all those muscle fibers out nice and long. you can also brine the chicken once the hanging is done. both of those things will help. and you can use recipes that cook slow and low temp. i dont know that you'll get quite the same tenderness, but you can get closer, and you'll certainly get a lot of flavor from it.