Here are some more perspectives from a "sales guy"
Regarding the path to FI, engineering my have a slight leg up because of the higher income in the early years. I think it took me 6-7 years to start crossing the pay of my engineering buddies. I have some solid savings habits, but will be a year or two behind on hitting the financial independence dates. I've been working for 10 years but only significantly out earning an engineer over my past three.
I think this is contributed to two factors:
1) Even if I have the same lifetime earnings 12 years into working as the engineer does, taxes probably take a more significant bite out of my lifetime earnings since the rates go up dramatically and you loose deductions and tax shelters (roth ira) when you earn a high income in a year.
2) You loose the compounding effect of those early savings. I am sure my engineering friends making 50,000 ten years ago to start saved more than I did making 34,000.
Regarding the "older" sales guy working - Some of the perception is true, but you have to also consider that sales can become a lot easier each year and the income generally keeps going up, especially if you're in a business where you are making recurring sales to the same customers.
Its hard to give up a job where the people you're interacting every day with customers who are generally your friends or acquaintances (because over 20-30 years you naturally migrate to interacting with people you like), have a lot of freedom in your job because you produce revenue for the company, have a nice client entertainment budget, and make in excess of six figures for not working *that* hard. This is why you almost never see older financial advisers or insurance agents retire. They can take almost as much vacation as they want and still keep their income.