The issue as I see it is that knowledge in any subject is protean. It changes. So if you wait to long to go back, what you learned before would be completely useless and you’d effectively have to start from the beginning.

Heck, the things I was taught in my Archaeology Degree from 2001 are at best, incomplete, and in some cases, now completely refuted. If I had left and decided to go back even ten years later, the technology that was suddenly in use alone would force me to start all over again.