Those spots don't look like much; perhaps some splash from when you watered them?? Hard to say, but a lot of my lower leaves end up suffering the same fate which I attribute to inadvertent water splash.. I think you're good!!!!
Also, the tips of the new leaves tend to look like that, so you shouldn't confuse it with nute burning.. Nute burn literally looks like brown, crunchy tips.. I've always been a bit of a fan of leaf tip burn, because if it only goes that far, it means you're riding the fine-line of maximum nute uptake and being too hot for the plant (so long as your pH is straight)..