IEP at age 15:
When a student turns 15, the student must be specifically invited to attend the Individualized Education Program (IEP) meeting and the IEP process begins to include discussions about life after high school. These transition components of the IEP focus on the development of three post-secondary outcomes: education and training, career and employment, and all other aspects of adult independent living.

• For information about Transition Requirements: http://www.cde.state.co.us/cdesped/transition_requirements 

IEP at age 18:
Parents Rights to Educational Records 
The Family Education Rights and Privacy Act, FERPA, gives certain rights to parents 
regarding access to their child’s education records. These rights of access to records transfer to the student who has reached the age of 18 or is attending any school beyond high school. Parents may still access records when a student over 18 is a dependent and is at the high school level or is receiving special education services.

IEP at age 21:
Special Education Rights
The parent’s rights defined in IDEA transfers to the student who is still in public education at the age of 21. Even though many other rights in Colorado Statute transfer to the student at 18, special education rights remain with the parent until the student reaches 21 as long as the student is in public education. These include permission for assessment and placement. All rights transfer to the student at 21 unless guardianship has been awarded. IDEA requires that school personnel inform the parent and the student of the transfer one year before it will occur. 

Learn more here: Transition Components of the IEP