Johndeereboy
I have done what you are asking. Several years ago, when we had serveral calves at one time, I put nylon rope halters on them between 3 - 6 weeks. I feeding cows everyday, and running them in the lot. I just caught one calf at a time, haltered it, and let 'em go. You have to be real careful that they don't wrap the halter around a tree, or bush and get themselves into a tangled mess. On the other hand, it allows you to run the calves into a smaller area, and easily catch them by stepping on the rope. You can scratch and pet them all over in just a few days, and even start tying them up in a week or so. Within about a month, I had all of mine where they would wait at the gate, run into their feeding area, and stand next to the rails waiting to be tied and fed. I would lead them out one at a time. It was pretty handy. I used those calves for my daughters to practice their clipping skills.
Good Luck with the Calves