Answer:memory decay
Explanation:which causes you to forget those things that your mind may categorize as not important or it may occur as you grow up that some memories are lost on the way as you accumulate new memories on the way to adulthood.
As the person grows up the mind eventually remove some memories to open a way for some new memories as it can be seen that Oliver was still young back then and also it is easy to forget things one don't talk much about.