Is it possible to develop reactive attachment disorder as a teen/preteen when they were normal before?
No. No, reactive attachment disorder (rad) manifests earlier. However, a teen certainly could have multiple signs and symptoms of rad. Conduct disorder, substance abuse, or a mood disorder all share symptoms in common with rad and are disorders that often have their onset in the teen years. Another consideration is that, in normal development, adolescents shift attachments from parents to peers.
Unlikely but... Reactive attachment disorder starts early in development and develops progressively, so the problem does build up. However, if the "quieter" symptoms like social withdrawal are not recognized, onset of overt symptoms may seem sudden. For a full description visit: http://www.Ncbi.Nlm.Nih.Gov/pubmedhealth/pmh0002514/.