I was on Ritalin until I was about 11. At 12 until now, (They increased dosage as I got bigger) I've been on Concerta. As i've read, it's an adult medication. Should I have been taking it?

Concerta is FDA approved for children. I'm not sure if it's even been FDA approved for Adults yes..

Like Tara said,
Concerta is approved for up to 18 years old and they are doing trial on adults. Even if it were not approved, doctors can prescribe "off label" to populations not approved yet or for other disorders.

My son is 9 and he takes 18mg of Concetta every morning. To early to tell if there have been any changes due to it.

My Kid has been taking Concerta since she was 9.