Directions are usually on the tag at bottom of bag. It's usually 6 to 8 weeks of age.
If it's 18 to 20% Protein, you can feed till 18 weeks or the first egg.
I feed a combo Start and Grow/Starter-Grower feed.
I feed Medicated till 10 weeks, then when bag is empty I switch to a Non-medicated Starter-grower or a All-Flock Crumble. GC