I was rather fortunate in this respect. I knew in grade school I wanted to be an astronaut. By junior high I had learned that chubby kids with glasses don’t get to be astronauts… but US Navy submarines were close to the same thing. [Side note: three former USN submariners are astronauts, the latest being LCDR Kayla Barron. She has submarine insignia on her NASA uniform. Of course, this is 50 years later. < sigh>] By 11th grade I knew where I was going to school, what my career path would be after graduation, and what my career options would be ten years after graduating high school.
In year 6 of my Grand Life Plan I was in an airplane crash. The GLP got fluid after that.
Plans are good. Flexibility is VERY good. 😁