Well it can be both, it just depends on how the term is being used. You would say "My daughter is 2 years old" or "I have a 2 year old daughter".
It depends how you construct the sentence. You could say, "My horse is a two year old." or you could just as correctly say that, "My horse is two years old." Many people use the same sentence...
24 months
STUPID! Of course it impossible!
No a 12 year old is too young and should be 16 before taking care of a 2 year old.