The average age of a matriculant is more like 23 or 24 now. That means that it's completely traditional to have a few years' activities outside of college before you start med school. Thus, not immediately applying to med school after college doesn't make you a non-trad. Doing a postbac immediately after college is just more college. Working for a couple years isn't a career. I don't even think the Peace Corps or military service makes you a non-trad, per se. (These are great EC's.)
In my mind, non-trad status is defined by two things, and a non-trad has to fit at least one:
First: a non-trad has one or more maturity-inducing responsibilities that would derail the average 19-24 yo premed from the ambition to pursue medicine. This would include things like having kids, having a responsible career that pays stable money, owning a house or business, being responsible for the care of a relative, or otherwise having at least one big adult responsibility that you can't just drop to go to med school. If you've only ever been responsible to your parents, you're hardly a non-trad.
Second: a non-trad has either been denied, or has passed up, the opportunity to pursue medicine before the age of 22-25, and has to sweat to get back in the game. About half the time, this seems to mean that the non-trad slacked during college and doesn't figure it out until several years post-college. The other half of the time, this seems to mean that the non-trad worked his/her fanny off for a career that he/she doesn't really believe in, and wants to move his/her talents into medicine.
It seems like money should be a factor, but I don't think it is. A kid who screws around until they're 28, and wakes up hungover in Thailand realizing they want to be a doctor, and has a trust fund they can use to get going on that goal, yeah, that's still a non-trad.
A lot of non-trads have made "mistakes," but this doesn't define non-trad. NJBMD is a good example of this: she left a thriving academic career to start med school at 45 or 46. There's no mistake in there. A 21yo who has a bad GPA and has to do an SMP to get into med school isn't a non-trad.
In my mind, being an immigrant is almost enough to make you a de facto non-trad, even if you apply straight out of college. Having to learn English at 13 and still excel in school fits my first "maturity-inducing event" category.
Lastly, having parental support doesn't prevent somebody from being non-trad. It's "sexier" to be an independent non-trad, but going back to school at 27 on your dad's dime, or having your mom around to watch the kids, doesn't reduce you to a 21 year old.
That's my $.02, to be taken with the usual bucket of salt.