I've banded goats. I don't recall the exact age, but it was less than six months. I was up for learning and told that they weren't bothered by it. In fact the two that I did jumped up, seemingly happy, and bounded away.
A few hours later, though, I happened to walk by the pasture and noticed that both were laying on the ground, panting heavily. It wasn't hot. I'm pretty sure they were in agony. I wouldn't do it again.
Later I found this; similar experience but told better:
https://www.ted.com/talks/mike_rowe_learning_from_dirty_jobs/transcript?language=en