Yeah, you can eat any chicken at any age. There are some issues with that though. One is how you cook them. We all have different tastes and standards. What is tough to you may not be all that tough to me, especially if you are expecting to cook them and eat them like you do the chicken you buy at the store. Those are maybe 6 to 8 weeks old and are really tender. If you process yours at that age you can cook them the same way and they will pretty much taste the same but there won’t be much meat there at all. I don’t know what your tastes are but I let mine get a lot older and cook them longer at lower temperatures with moisture.
The other issue is how much meat you get off them. It sounds like you have pullets. If I remember right Amber Links are those little sex links that are based on the commercial egg laying chickens. They are purposely bred to not get very big. If they had a big body they would have to use feed to maintain that big body. That’s not cost effective if all you want is eggs. If those are what I think they are, you’ll never get much meat off of them. They are not real efficient at converting feed to meat. They are bred solely for egg laying.
Some people process non-broiler chicks at 12 weeks. You can still fry or grill those but there is not much meat there, even on regular sized roosters. I personally wait until they are at least 16 weeks old and prefer older. I hatch eggs so I have male and female. The cockerels get eaten first. Most of my pullets get a chance to lay before I eat them so I can evaluate whether they wind up in my laying/breeding flock or wind up in the crock pot.
I don’t have a perfect answer for you. I think a lot of it is personal preference. You can try one at 12 weeks and see what you think, but realize there will be some development in the next month. With those pullets, there won’t be a lot of meat development no matter how long you wait.
If they are foraging for most of their food, it doesn’t cost all that much to keep them, but if you are buying all or most of what they eat, you are probably better off eating them young and use the money that would have gone on feed to buy chicken from the store.