So is my climbing perch cozy in this tank size. He is still juvenile like 2.5 inches.
Definitely not. There are several fish commonly sold as Climbing Perch so it would help to know which one you actually have. The true CP grows to about 8-9", and would need about 50 gallons or more. You also need a mature cycled filter on the tank (whatever fish you have in it), and a heater to maintain a steady temperature.
What size tank is it?
Im sure this is a climbing perch not a leopard bushfish this is the anabas testideneus and I did not buy this someone caught them near our property and they were injured but I can only afford to take care of one and he is still a juvenile not the whoppers you see on Thai markets.
He may not be large now, but he will grow to be that large. He needs a bigger tank now.
Yes, waiting will be a detriment to the health and growth of the fish.