Can I immortalize baby's iris?
No, not like that. A baby wouldn't be able to sit still and look in the right place with the slight discomfort that the light can cause on the eye.

 

From what age can you have your iris immortalized?

There is no real age, but the child must be able to follow instructions such as:
Take the right position on the head support, look in the right place (and it is not so easy with a lens that is only a few centimeters from the eye), open the eyelids wide and above all remain still while respecting them.
For example, I have never managed to capture the iris of my youngest 4-year-old daughter with the level of quality that I wanted. The quality of the photo will depend on the respect of the instructions.
 

Can I immortalize my pet's iris? 

No, just like for babies, it is not possible to use this method to photograph their iris.
But it is possible to take pictures of their irises in a different way, but everything will depend on the animal's ability to remain still. Example with the photo of my cat's iris.