Is this a deficiency?

Considering the early stage and how the deficiency shows in a proportional way in the leaf internerves and also on both young and old leaves, it is probably lack of magnesium or micronutrients, such as Iron and Manganese. How are you fertilizing it?

It looks like an early stage calcium deficiency but with little to no information on your grow it’s too hard to give an accurate suggestion on what the problem could be.