First off Welcome to the Board. and here are my best answers to your questions. You could possibly estimate his age by letting us know where you got him from? If you bought him on aquabid or something from a breeder he is probably around 3-5 months, but it probably would have said that in the auction. If he came from wal-mart/lfs/lps then you are looking at a betta that is probably at least 8 months old if not a year. These would be considered "grown up". They are past their prime age, and are considered pretty much full grown. As for decoding betta language, I really have no idea, but I think you can tell when one is happy or not, by how active they are, how they react to you as their caretaker, and such. It sounds like your boy is a happy camper in his new tank, and we love pics around here so post post post!!
