From your other posts, I think you may have an unrealistic expectation of how much grad students make. I saw your $16K/month figure. As said above, most grad students in the sciences make just enough to get by - usually living 2-4 to a room and eating as cheaply as possible. Outside the sciences, the situation is even worse - most grad students need to take out loans to pay for school.
After you graduate, let's say with a PhD in physics, the situation gets better, but you are still not wealthy. If you are working towards an academic job you probably need to be a post-doc for 4-6 years. These pay better, but probably still only in the $40-$60K/year range. If you take a job in industry, you might have a starting salary in the $60-$90K/year range, but this would still not be enough to pay off student loans in a matter of months.
Others might want to comment on whether or not my figures are reasonable.
Where did you get your $16K/month figure? This is the type of salary that someone in the sciences might only make after many years of experience, if ever.