When should I move him to bigger terrarium

I've had my baby beardie for a little over a month now. He is still in a 20 gallon long, but I recently got him a 48" enclosure. At what point should I move him over. He is still only about nine inches long.

Some beardies may be different than others but when i came home with my juvenile she was 4 months and around 10 inches head from tail and i moved her into a 55 gallon right away. She did great, ate well, active and did everything that shows a healthy happy beardie.

I then moved her to a 20 gallon as another reptile had to be upgraded to a 55 gallon, she was not happy about the small space at all and lived in there for a couple more months until i got her a 75 gallon, and shes never been happier to have so much space once again. Beardies truly love space.

You could probably upgrade now as long as he does good in it, active, eating, basking ect. He may become a little bit stressed because of the new environment but it should only last for a few days or a week at most.