Just giving you a guess. Sounds like it needs fed. What fertilizer do you use? There are some safe natural types out in the market. Like fish poop, kelp, sea-weed. and so on. Google natural fertilizer. I don't like to recommend chemical types due to burning the plants.

I do not know about need for fertilizer - I am louzy at that (have 2 agaves, and I am not sure they got fert 3 or 4 times since I have them, almost 6yrs.) It is possible.

Another possibility - it seems to be oldest leaf. Sooner or later, old leaves will dry up. It takes long time, but they dry up to almost paper-like, and could be taken off or just fall off.

Here is photo, just taken, of my Agave F076 with old, dry up leaf. It is now last leaf on plant. In 6yrs, this is, I think, leaf #6 - but I am only guessing since I didn't keep track. I have also Agave ferdinandi regis, and that one didn't have any dry leaves yet (same time). But it it also smaller, and I think younger plant - not sure.

I have it potted in a mix of grit and perlite (about 1:1). It is under lights now, and outside, in sunlite, during appropriate weather.

How old is your plant? Did you change anything recently? Is soil draining well?

Your poor Agave friend is etiolated. Not sure what the yellowing is, but the main issue is it needs more light. Agaves need lots of sun and indoor filtered afternoon sun is not enough. I’m guessing you live in a climate that’s too cold to keep outside? There are a few succulents that I don’t think should be grown inside and big Agave are one of them. To get this thing growing right you will need grow lights. But imo this is not the species of Agave to be grown inside to begin with. I’m pretty sure your Agave is americana and they can get huge. I’ve got one now that’s about a meter tall and it has plenty of growing to do.

Another issue is it being grown in a pot. Agave americana has a huge root system that needs room to spread out. My neighbor has a potted A. americana outside and the poor thing clearly hates its life.

I’d bet the farm that his Agave americana would be much happier in the ground.

Agaves are tough plants and yours is hardy down to zone 8. Could you possibly put it outside? I don’t have a crystal ball, but I’m pretty sure if your Agave doesn’t receive stronger light you’ll probably always struggle with it:(.

I’m not trying to rain on your parade, but just trying to help.

There are smaller species of Agave that would not take up so much space and I think would be a little easier to grow inside with a grow light.

Like this guy below is about 6” wide.

There are dwarf Agave that are tiny. I’ve got one that’s around 3” wide.

Anyways a grow light is a must if you can’t put your Agave outside. I know nothing about grow lights, but I‘m pretty sure you will need a strong light set up to get your americana on the right track.

Goodluck:)!

Kara and Rina gave some good advise.

I don't think your agave is Americana. Looks more like A. tequila. I live in Zone 6 and have way too many agave. I had A. americana and it grew very large and did extremely well for me with out any special lighting thru the winter. I do keep them out side 7 months our of the year. Now I keep them with supplemental LED lights. Walmart shop light.

I did have to give up my A. americana due to it getting way too big and too hard to move in every year. So what did I replace it with; even more larger growing agave. I know I need help but not going to get it here.