I think 2 yrs is not too young. No references for you, just past reading and family experiences.
My sister had CP around 20 mos. It was very mild for her, but enough of a bother that she was not comfortable in diapers. Turns out she was very easily potty trained while she had CP.
Younger than 1, I would not feel comfortable with an intentional exposure. Between 15mos and 4 yrs I think is ideal. The older they are, the more they tend to react/have a worse case.
DS, 10/07. Allergies: peanut, egg, wheat. We've added dairy back in. And taken it back out again. It causes sandpaper skin with itchy patches and thrashing during sleep. Due w/ #2 late April, 2012.