To the best of my knowledge, such a salary spread in engineering would span different jobs with different job titles. Inside software engineering, you don't get promoted from Junior Software Developer to Architect by seniority. Heck, being a senior citizen doesn't even guarantee you a promotion to Senior Software Engineer. Outside of software engineering, only about 5% of people earning engineering degrees end up doing design work at all, so the work roles of different engineers can be very different.
You have a good point about retention in the early years, which is why I mentioned five years of experience. I also believe that the best teachers just keep getting better. However, among average teachers I couldn't tell much difference between the thirty-year-olds and the sixty-year-olds, except that the thirty-year-olds were better-looking and told better jokes. I had dozens of teachers and cared deeply about the performance of each one (me: valedictorian, mathlete, AP whore) so I expect I would have noticed the pattern if older teachers tended to be significantly better than younger ones.
To the best of my knowledge, such a salary spread in engineering would span different jobs with different job titles.
I've lived the 50K-100K salary spread for the same programming job. Also, at my last "real" job Amazon stole away one of our interns. He was offered a job for $86K whereas the other intern was offered almost the same position for $67K. She was the better of the two developers. I'd like to believe there wasn't any gender discrimination going on with that situation, but I don't.
Anyway, there's definitely huge spreads for the same work in software. Sometimes, even in the same company! In my experience, salaries are completely arbitrary for software engineering. I've gotten paid the most for the easiest work I've done. The only constant I've seen is that salaries are higher across the board when the economy is good.
You have a good point about retention in the early years, which is why I mentioned five years of experience. I also believe that the best teachers just keep getting better. However, among average teachers I couldn't tell much difference between the thirty-year-olds and the sixty-year-olds, except that the thirty-year-olds were better-looking and told better jokes. I had dozens of teachers and cared deeply about the performance of each one (me: valedictorian, mathlete, AP whore) so I expect I would have noticed the pattern if older teachers tended to be significantly better than younger ones.