It's totally fine. They grow in moderation, and I had one in a 20 for a while. Ya, let him grow with you. take all the pics you can, lol. Dont wanna miss his first run in with the side of the tank or those first few strokes of his fins, lol. 29 is good for a year, then definitely a 55. I have a 55, my yellow tang is doing fine. he loves it. They will live 2-3 years I think. Have fun:joy: