I love animals.
My too. Especially armadillos. It means little armoured one in Spanish. 
Yes they are so cute and odd looking.
Yes, they are. All species of armadillos are native to the Americas. 
Why do they have the hard shell?
More then likely because they are a decedent of an extinct group of mammals, know as glyptodants. 
When was that around?
The linage of armadillos go back some 35 million years!