I grew up an orphan. My parents both died in a car accident when I was 5. 
Sorry! So pathetic! So who's an orphan?
An orphan is someone whose parents died or permanently abandoned them. 
At what age bracket could one be regarded an orphan?
In the United States an orphan is a minor -- which means under the age of 18. If your parents die after you are 18, you are not technically an orphan. 
Are there laws related to the adoption of an orphan?
Yes, there are definitely laws for adoption because it's a permanent change in status. A less formal arrangement is guardianship.