So if I were to get a baby and thereby start it out in the 10 gallon, what's the average estimate to when it gets big enough to move into the bigger 30 gallon? I know it varies considerably depending on gender, feeding rate, genetics ect., but just for humor's sake if you spitballed a number.

And on top of that, is it generally better to get a baby compared to an adult? Since then it grows up with you and such (and of course the joy of watching it grow).