18 & Up
18 if you have no criminal record. so be good. The age when one is eligible to adopt a child is determined by the state law in which the potential adopter lives. However, there are a multitude of...
Really You are never to old to adopt, or do anything.
Depends on where you live. Some allow from 18 and others not until you are 25. If you are related to the child that can also play a role.
I think you haven't to be 19 or older =)!