Why are the lower leaves turning brown. The top looks good. Also some brown spots on other leaves.
Brown Lower Leaves on My Agave Potted Plant
Certified GKH Gardening Expert
This appears to be a spot from iron deficiency. This can be caused by, either, an actual lack of iron or too high of a pH.
You can add iron sulfate to bring the pH down, and use dolomitic lime to keep the pH more stable over a long period of time.
Here is an article that will give you more information on the plant: https://www.gardeningknowhow.com/ornamental/cacti-succulents/agave/growing-agave-plants-in-pots.htm