This mirrors my experience, everyone I knew who could speak Spanish well when we were around 4-5 years old, still can 30+ years later even if they rarely speak

This mirrors my experience, everyone I knew who could speak Spanish well when we were around 4-5 years old, still can 30+ years later even if they rarely speak it with anyone at all. Now nieces/nephews who might pass for fluent to some when they were 4-6 yr, after only 2-3 years after going to school can hardly form the most basic of sentences and cannot communicate with their parents/grandparents at all. All of this is under an environment where only Spanish is spoken at home. They can still understand it but will probably forget that aswell in time. The conclusion seems to be that those that are fluent do not forget but those who werent do. I suspect the author considered being able to communicate with her parents as proof she knew the language. Parents can communicate with their children perfectly fine where others would struggle to understand a single word.