No he is not ready yet to head out to the coop. He is close though. When they are about 5 or 6 weeks old, they won't need the heat anymore and can head out to the coop. Make sure your brooder has enough room as they do grow fast. But yes, they do get "brooder fever" after a while. You can take them out for field trips outside or to the coop at this age. As long as the weather is nice, over 50 degrees and not raining, they will enjoy getting to roam around for a while in the grass or in the coop. Keep it short outside at first with 10 or 15 mins on that first time. You can increase the time as the days go by. Always supervise at every moment and never leave them alone outside as they are hawk bait and can get lost very easily at this age.
Good luck with your new babies and welcome to our flock!