Quick question....

Is it possible to be too young to be diagnosed with DID? I've looked all over the internet and can't find the answer.

not sure either. we know one system for sure who were officially diagnosed in their teens. but most systems we know took a lot longer to realize what was going on.

I think that Ts and docs in my country are slow to diagnose DID before age 21 because that is the age when they can officially diagnose a personality disorder here.
adolescence brings a lot of troubles, difficulties to self-regulate and insecurities about identity. they want to make sure it is not that, but that a "fully developed" person past adolescence is showing these symptoms.