I don't remember reading about a specific age....I've never done one before 8 weeks, and usually 10-12 weeks. However, just mo, I would think that if they are sturdy and healthy enough for vaccines, they would be able to tolerate the chip. It's me that can't tolerate doing it when they are smaller.
I don't think I would ever do one under 2 lbs, but I have absolutely no basis for saying this, just me. The same chips are used for much smaller animals, so I think medically there wouldn't be a problem.
The instruction sheet that comes with the chips indicate that it should be placed between the shoulder blades, in the trapezius muscle. It was pointed out to me that their site says it is subcutaneous....which as you probably know just means under the skin. However, if it is only under the skin, the chip can migrate to other areas. (which for obvious reasons is not good) If you place it just into the trap muscle, it is stationary, and yet not too deep so as to hurt overmuch. You do it at a slight angle, so that the chip slides in kind of sideways, and not straight down into their body. It is a little tricky getting used to it at first, but after you get the hang of it, is ok. It would be best if there were someone in your area who could demonstrate for you; this is what I had at first.
Once you get the hang of the angle and placement, it's one of those things that you do quickly and decisively....kind of like how you would give a shot to a kid--know where you're going and get it done, but not too roughly.
<sigh> I wish, wish, wish I could whistle.....
