Josh, my chams see 3 cage sizes throughout their life and i think having a cage that is tailored to the size of you cham will be best for him/her. A 3 month is pretty small. I keep my babys in 15x16x20 inch cubes until theyre 4.5 months old then i move them up to 15x16x30s and then to a 2x2x3 after about 7 or 8 months, females a little bit longer. If your cup feeding him he should be ok in a 15x16x30 until hes 7 month old or so then he'll need his adult enclosure but i strongly urge you dont put him in his adult enclosure just yet. If you put him in a 15x16x30, remember to keep a close eye on him to ensure he is eating properly and you should be fine.