Some may say medicine. I do not think so. It is expensive to become a doctor and you might just end up paying your debts a few years after you graduated.
Medicine is not as expensive as you painted it, my friend, a little money added to an average program will hand you that certificate in most countries. Besides, have you thought of a scholarship? If you are brilliant and seek for scholarship to study medicine, the chance of you being sponsored is high.
I say information technology or Computer Science.
I knew this was what you would choose, well, it's good if you are good at it. The truth is that not everybody has that coding brain, so what should become of them?
a person needs to study for 15-20 years as minimum.
20 years to study medicine? Which country is that? 6-7 years is enough to study medicine, others will be paid-practical training, so you have nothing to lose as you are already earning. So long as it's what you want with your life, why not? This wasn't even aligned with my former response, which focused on the fact that money shouldn't be a barrier to studying medicine if the person could afford to pay for other causes.
Lets start with which area of medicine you are talking about? Within 6-7 years who you will be? In our European country its a nurse (study + practice for which you will earn minimum wage). There are not scholarship or there is something like 2-5 places among 150 students. Can someone become rich by working as a nurse?
Lets take other medicine profession that is highly paid. Dentist. Checked quickly info about studies. 6+ years to study (during which 4 years you will be practicing on manikins) and it cost +14k per year to study. After that you will become only dentist assistant. It will take years of practice before you will start earning well and turn default city dentist into someone who people stand in queues to get in.
Surgeons earn a lot. Think they possibly are the one who can be called as rich, when they retire. I cant even imagine how expensive it will be to study, and how many years it will take.
Or, I am very desired to hear your comment which profession in medicine can make a person rich, it wont cost "like a Boeing wing" to study, and study process will be short.
P.S. My cousin studied computer science. He paid around 2k EUR per semester. Took him 4+3 years to get to MBA. Works as an IT in a bank with a salary around +2.5k EUR.