My stepfather and I both have dissociative amnesia - I'm 19 and my memories are coming back and he's now 65 with memories still coming back, having only started to remember a few years ago. There's no set 'age' for when they come back, and for some they never remember at all. Not only can the amnesia happen for trauma at any age, but the memories can come back at any age.

Like the previous poster said, I think you should believe in yourself; everyone experiences this differently, and just because it isn't the most common experience the therapists have seen doesn't make it any less real or valid