I was told a 30 long would be good for life. Mabey a 40 if it gets a little above average in size. But also babies and young balls are also afriad of open spaces, so a divider should be put in the cage. A little less then half or so. Once it is older (I am not sure about what age, I think mabey around 10-12 months) you can start to move the divider back a couple inches every few months. I got a cardboard divider in my tank. Make sure it is wedged tight so he can't move it and make sure it goes all the way from the top to bottum. I left 1 inch open from the top and one day I found him stuck on the top of the cardboard.
