Thank you.I would say 2 years max? At minimum I think they require at least a 6 foot length. However I’ve seen many arowanas in 4 or 5 feet aquariums but I don’t agree with it
How long would it "last"? They are a super-tough fish, so depending upon maintenance, water changes, etc. it could probably survive for a long time.
But since they are also very fast growing, and assuming/hoping that your goal is a better life for the fish than mere survival, I'd say a year or so.