The rooster I chose from my batch(pure Barred Rock) was one that wasn't picked on(not a sissy) and didn't pick on others. I wanted to keep one of myI eat them, once they are no longer tiny fluffballs.
What age and weight depends a lot on how they are acting:
If they are annoying me with too many crowing at once, or if they're all pestering the pullets, or if the pen just seems too crowded, I will butcher them sooner.
If everything is going fine, and I just don't feel like deciding yet, I will butcher them later.
I prefer to butcher some of the obvious not-keepers sooner, and wait until later to make final decisions about the last few.
My obvious not-keepers would include any that I consider ugly, any that have physical problems (crossed beak, wrong number of toes, things like that), any that bite me or attack me, any that regularly get out of the pen, any that are so submissive that they don't get enough to eat, any that otherwise need special attention.
If I pick each male up to look at him, and if several tolerate it calmly while one panics and struggles wildly, the panicky one will probably get butchered.