This Puya can get larger if you let it and I do have one in a 3 gallon pot. But if you keep it in a small pot it will stay small for a longer time and flower like this one is doing.
I don't like this plant much brcause it has small spines that come off easy and are hard to remove plus the flowers do not last that long. It will make seeds with out any help if you would like more of them. Oh no.