Correct me if I'm wrong folks, but 3 mo. old panthers are still pretty small compared to a let's say veiled. I have my 3mo old panther in a 12x18x20 and she still has trouble shooting her food. I will be adding more branches/vines so she can get closer to them. After all, the tongue is still short. I understand that tongues can shoot 1 1/2 x 2 times the length of the cham.
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.
4ft tall is way to large for a 3 month old. Thats an adult enclosure... Food would be an issue and he would wonder in and out of the range of uvb he needs, especially at a stage in his life where he is going to grow like a 3 month old does.