normally, the creep gets put out from when the oldest calf is a month old, until the youngest calf is weaned. historically, we also wean as close to 5 months of age, but yet the whole group, or most of the group at once, so some are younger, and some are older. This holds true for calves born all year long.
This fall, I did something different. It was the first year we did not creep anything, and I had one youngster that I weaned at 3 months of age. no creep, and I pulled him from the cow and put with the big calves on a self feeder. Here we are about a month later, and he's finally starting to come on pretty good. It was my experiment, and for the most part, I'd say it was a success...
With that said, will I be weaning all my calves from now on at 3 months, no- but I won't hesitate on the occasional calf that's born at an odd enough time to be a pain if left on the cow.