One thing i noticed is how he has an eidetic memory so he would remember the age he got into Comic Books which was 9 in Young Sheldon so he'd remember that cause he remembers what ages he was in each grade right
But when he gets a new wallet and has to get rid of something from it lenard says how about his honorary Justice League of America card and he says he's had it in every wallet since he was 5 but apparently didnt like comics till 9