i would say "3. Working in real projects at industry" when i was 19 i had the opportunity to build real world systems. Durning that year i delivered a full stack e-commerce using MVC pattern for a client. Someone who is just starting its a lots of hard work to deliver a MVC full stack app and i learned a great deal.

Later i joined a USA based startup really large project. This is where i learned how to manage large SaaS apps and how to manage complexity.

Since then i have been only building SaaS products and i love it. Currently i am leading the development of microservices based system based on GraphQL and everything is running k8. i have worked on every part of that system.

I think starting early helped me a lot :)