Usually I wait until the pup is a year old BUT if you feed a large breed adult food, you shouldn't have any worries. My breeder says she usually keeps the pups on LBP until 6 months old and then switches to adult food. Doing that shouldn't cause any problems.
Shasta GSD 5/5/10 CGC, ITD, TC
"Dax" Thor z vom Weberhaus BCAT CAX2 CGCA ETD HCT NCO-1 PKD-T RATI RATN RA TC TKA 3/18/2013
"Hades" Guilty vom Blutfeuer 10/26/2018
Zena GSD 6/1/03-2/16/2016
Riley GSD/BC 1/10/05-2/1/2013