Some BP are easily stress and you will see signs right away, some it takes a little longer.
I would not move this BP in a bigger tank until he is fully grown if I were you even then, it is still more space then your BP will ever need, adults do not require anything bigger than a 30 gallons (L: 36.00 W: 18.00 H: 12.00) glass tank.
Keep in mind that the bigger the enclosure the harder it will be to maintain proper temps and humidity specially during the winter.