I'd be cautious about getting another dragon to house together with your existing dragon. The main concern I see is a 5 month old dragon is nearing sexual maturity and the age where he will breed. If you place a female in there he's going to attempt to breed her probably pretty fast. That's pretty young to induce a male into breeding (even though it wouldn't be on purpose).
If so, the female must be of breeding size, age, and weight. If you add another male they will most likely fight either right away or within a few months due again to sexually maturing.
A 48" x 24" x 24" is fine for housing two adult females that get along or a breeding pair of dragons if they are of appropriate age, size, and weight.
Goodluck,
brandon
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Dragons by Nature