I've done a fair bit of mentoring, but I see that as a non-technical role.
When to start optimising and when to stop, debugging and fault finding approaches, why clever code is stupid etc.
Almost pre-internet academically I started in 1976. Commercially as a programmer was 1987 ish

It wasn't wasted, you know how not to do something, a very valuable lesson.
One I wish those twenty somethings had been taught as part of their vaunted education.