Yellow lower leaves on 8-9 week old plants - Deficiency or age of plant?

Looks like an overfeed to me on the flowering plant though if the yellowing leaves on the veg plants are towards the bottom of the canopy and then work thier way up usually its a sign of nitrogen defiancy just give her some more veg feed and she should pull through autos are some of the trickiest plants to feed they always like very little to begin with then in the first few weeks of flower they want everything it can be hard to keep on top of and your certainly not alone also with the overfeeding its very very common towards the end of a grow just make sure you extend your flush by a couple of days and you should be fine :) best of luck brother.