In BA FO's have 2/3rds the aircraft limits on all types.
There are no varying degrees, its 2/3rds for all from day 1, or you don't make the line.
Obviously the captain has to use his judgment as to the experience of the FO, but in theory its from day 1.
Incidentally I let my FO land it yesterday up to his limits with windshear and turbulence under 100'. Did a great job as I knew he would.