If it is just the older leaves then the tree is getting ready to sacrifice them for the health of the tree and newer leaves. It may be time up for the old leaves.

I would say around 40% of the leaves changed like that, so a lot.

Magnesium deficiency, epsom salt worked for me on my Meyer.

not sure this is Mg deficiency though, may be just old leaves. Regardless, some citrus micronutrients foliar spray wouldn't hurt.

So my tree is in ground and there may have been a general fertilizer working as well. I think I put a couple tbsp of epsom in a gallon of water and dumped it under the drip line. My tree looked exactly like this and after application the classic V pattern from leaf tip on older leaves went away. A magnesium deficiency only shows on older leaves. Manganese will show on new leaves for instance. Magnesium deficiency is more likely to show up in seedy varieties. I believe Meyer's are notorious for showing deficiencies.