It's good to see someone else here with a big goliath.
Lots of other people who post on here don't know much about keeping fish and kill these fish before they get to a decent size...I remember meeting a guy who wanted to buy some of these from me but didn't even know what a canister filter was...what a tool!
Or they sell them off when they're broke and the next guy's fish kills it...I've seen a few people cry about that...LOL!!!
Mine is 2 feet long and I've had it for 6 years since it was the size of my pinky finger.
Good luck with yours and keep posting new pictures.
BTW, nice armatus...I used to have a 23" one which I grew out from 3" but I sold it a couple of years ago to a guy who had a much bigger tank than mine at the time.
Now I've moved and set up a much bigger tank and I wish I had it back!
Need to get another one.