OH, show chickens! Gotta love you people and your ability to make a chicken stand still! I can't...
I did bath a hen thou a few days ago, only cuz she was egg bound, and she was not so happy at first... Then she tolerated it. First bath she ever had. I just made the water body temp for her, and used my bath tub... Yeah. Not kidding. I tried doing it in a tote, and she HATED that, but was ok in the bath tub. Go figure... I also kept a hand on her practically the whole time...
I've had to bathe one of my chickens several times because she has had a nasty, poopy butt. I found a neat video on youtube through a link on this forum where the man was showing how to wash chickens to take them to a show. Here's the link:
I thought it was a funny but very informative video.
It worked very well with my pullet, although she was about 6 weeks old when she got her first bath. I can't comment on a minimum age, but I do know that little chicks can't regulate their body temperature so I'd be very careful of the temperature of the water and be sure they are nice and dry before they go back in the brooder.
The video showed a three step process with a bucket of soapy, lukewarm water (Dawn Dish detergent was the recommended soap) a second bucket with lukewarm rinse water and a third that had more rinse water but with white vinegar in it which supposedly gives their feathers an extra shine for the show. There were a few other "ingredients" to make the chickens more show ready but I didn't use them. I only used the first two steps, placing my pullet into the soapy water and just letting the dry clumps soften for awhile. She was remarkably calm about the whole thing although I did have a few frantic flaps until I found the best way to hold her. As the clumps softened, I gently worked at them with my fingers, careful not to pull out or damage the feathers. A couple of times I got a little extra detergent on the tips of my fingers to work on some really soiled feathers under her vent. It probably took 10 - 15 minutes before I transferred her into the second bucket (in this case my big pasta pot ) for a rinse. The water had cooled enough that I had to add some more warm water so I'm glad I was doing this at the kitchen sink where I could add more water as necessary. I kept the depth shallow enough that she could stand, but deep enough that it came up above her hind-quarters when she was standing with her legs stretched. After awhile she seemed to relax and sink a little deeper in the water but even then, her upper torso shoulders and neck were above the water.
When we were done, I held her above the sink for a few moments to "drain". A whole lot of water can come off a wet bird, and then placed her on an old towel on the kitchen counter and gently blotted her dry, not rubbing the feathers. We finished with a blow dry, the hair dryer set on low until she was nice and fluffy again. I've had to do this three times and each time she seems calmer about the process, so I take that to mean that she really didn't mind it much. I figure that if she really didn't like it, she'd struggle MORE rather than less when I start the process.