This is a general response since I haven't raised an aro, but it's a summary of many studies I've seen on fish growth. In nature fish don't grow all the time and periodic slow downs followed by growth spurts is fairly common for FW fish. Having said that, fish who "slow down" for too long, don't make up for that later, especially if it's the early part of a fish's life. Too long can seen as something which is longer than a year, certainly 2 or 3 years.
To maximize the chance for a fish to reach it's individual genetic potential in size requires a lot of things but clean, fresh water, plentiful amounts of nutritious food, plenty of space, and low or no stress environments are some basics. While each fish is unique, it's reasonable to expect that a fish should be able to reach 80-90% of the recorded maximum sizes for that species. In some cases, it can exceed that. Of course, that will likely take years, so it almost means that the commitment to a larger tank has to be made earlier rather than later if that is the goal.
