Answer:At least 18 to 36 months of age
Step-by-step explanation:
Jack must be at least 18 to 36 months of age as he agrees to wait to eat cookie though he was not happy.
Delayed gratification comes under this situation where a person tries to resist the temptation of an immediate reward in favor of later reward. Age majorly affect the Delayed gratification as children under 5 year of age show very least effective strategies for delayed gratification and it increases as we grow up by distracting the mind over another thing.