How do you fine someone that was in the Marine Corp?

Most veterans have a Marine Corps sticker, or keep their combat knife, or a saber, or their Dress Blues. Some even have a USMC tattoo.

Absolutely, there may just be some jobs that you are not eligible for. All of the jobs where you would be disqualified have to do with the aviation (pilot, ATC, ect.)

Extreme patriotism, feeling of ability to serve most effectively that way.

This really depends. You could find out through the friend of a friend who's cousin's friend's mother's twice-removed-uncle's son's niece's husband's sister's brother's cousin. But if you know their...

The oldest living member of the United States Marine Corps is Richard James Rhinehart of Baltimore, Maryland. He was born on March 10, 1908.