Answer:
Hyphertimesia.
Step-by-step explanation:
Hyperthymesia is the condition that allows people to remember an abnormal large amount of experiences that they've gone through. They also remember these experiences with an incredible vivid detail. This recall of situations of memories is not based in mnemotechnics but it just stays in their mind without any other helpful strategies.
In this case, Martin has a stunning memory of virtually everything that has happened to him since he was 4, he remembers specific details of his 6th birthday and 6th grade. He actually remembers this even after almost 50 years later. Therefore we can conclude that the condition he has is Hyperthymesia.