The sports of "Kichijokan" (of which "Desert Diamond" is one) tend to be excellent container plants.
Happy Crown Agave (Agave 'Kichijokan')
Agave (Agave potatorum 'Desert Diamond')
Happy Crown Agave (Agave 'Kissho Kan')
It will grow differently in a container compared to how it grows in the ground (smaller, slower, less prolifically). And the variegated versions of this plant grow slower than the non-variegated form. I doubt anyone will be able to tell you the increase in diameter per year, though. With small agaves that don't have too many leaves (like the one in your picture) you might expect a new leaf a month when they're going strong. Later on, close to full size, it might be more than that. Your plant might reach near its full potential (limited) size after 5-10 years under optimum care, roughly.
The size of the rosette is not something to aim for, necessarily. For example if you provide insufficient light indoors, the leaves may end up getting stretched, and the plant might look bigger overall as a result. But etiolation is not great for the health of the plant and it's something to avoid. Light is always going to be an issue with indoor agaves. To minimize this, keep your plant right in front of your sunny window and make sure it "sees" the sun for hours a day year round. This is particularly important during the shorter, darker days of late fall and early winter, when you should check the situation to make sure the sun is still hitting your plant.
You cannot provide too much light indoors.
skopjecollection said:So in a nutshell, get a more coarse soil, repot, dont water for half a month, and water weekly with a tiny ammount, less often in winter.
It might help to move your plant to a mix with more pumice/perlite/gravel in it, like regular potting soil with an equal volume of rock mixed in. And you should wait to water after repotting for a week, but 2 weeks is overkill. When it comes to watering your indoor succulent "less" than an outdoor plant, that does not mean less water but less often. It means watering to completion (generally, maybe not in the darkest, coldest days of winter) but doing it less often. Not watering your plant to saturation does not do you any good unless you're particularly worried about cold and dark conditions. Cold, dark, and wet is like a lethal trifecta for agaves.
Water well, until water comes out the holes in the bottom of the pot, and then wait until the soil is dry or almost dry at depth before watering again. The actual interval will vary with the weather and the seasons but it will tend to be longer in winter (maybe every 2-3 weeks) than it would be in summer (maybe once a week). Having more rock mixed into the soil will help the soil dry out faster and keep you from overwatering, which may lead to rot complications.