As a Christian is it usual to doubt religion as a whole in the mid teen years?

You are quite right in that people believe what they were raised to believe. When I became an adolescent, I did begin to question my religion and everything else. Now my son is doing the same thing. Do not be afraid to ask the big questions. I studied world literature as well as philosophy in my quest to find a sensible belief system. I came back to Christianity (although a different denomination) after 20 years of studying. Keep looking for the answers.