Gender atypical boys

Interesting blurb on a Japanese boy who was allowed to enroll in school as a girl. I wonder what some local school policies are in the US. At what age should children be allowed to transition? One website I found argues for pre-puberty hormone treatment for boys. From the site:

"Nicole Roukema (Netherlands) was born Neils but knew that she was a girl by age 3. Now 13 and transitioned, she plans to have SRS surgery when 18."