Critical? No.

Yellowing of lower leaves is common as the plant matures and starts to prioritize the upper growth as it gets ready to flower. It could use some nutrients, but it looks good overall.

It's a deficiency but not necessarily what you might be thinking. I'm gonna bet your going through a growth spurt and the flow of nutrients going up sometimes isn't fast enough for the plant to nourish the top so some of the mobile nutrients in the lower leaves move up. It's completely normal for the lowest leaves to be affected but you gotta keep an eye on it because if it progresses further up it's an actual deficiency in that it's not able to keep up demand with what it's pulling from the roots. This would be a scenario where foliar feeding can come into play to allow a localized uptake so it doesn't move those nutes from leaves to fill the temporary gap. And I say temporary because it could be less than ideal weather, ie cold roots or it could be the stems are too small or it could be a really tall plant etc etc etc.&

So just keep an eye on it but if it's giving you anxiety you can just scratch a little blood meal over the top, but go light.