21 months

? Thats nothing...
So full grown, how big is full grown? And how long is a long time? Thats the problem with those statements, they are not factual and usually bs. Just like everyone says my Oscar lived a good life, 8 years!.... please it died like half its life span early....
None of you can really say anything.... As none of you have an arowana over 24".... If you do, then you have a tank larger than a 240g... simple as that. Justification, its what society is now a days. My friends arowana is 21 years old, and theres a reason he is that old. I'd be surprised if one of you guys had an arowana for 5 years. A fish that gets easily 3ft in an 18" wide tank!? Once again, MFK is going down the hole because of people who can't give animals what they need.
No you don't need to be an expert on fish to keep them. You just need common sense and comprehension, the experts did the hard work for you. They posted a recommend tank size and still people are to stupid to figure it out...
?
On the end note, jars are different than silvers.. along with tank sizes
Ignorance is pathetic, done...