Depends on the specific type of doctor. But generally you're looking at:
4 yrs undergrad
4 yrs med school
Then residency/fellowship/etc. That's like minimum 3-ish years, but depending on the specialty it could be 7 or more years residency.
So you could easily be into your 30s before actually having a job.
earned your bachelor’s degree
graduated medical school
completed a residency
at least 11 years would have passed.
Before The Game: Earn a Bachelor’s Degree – 4 years
Intense Training: Medical School – 4 years
In The Ring: Residency – 3+ years
Pick a major that interests you so you don't mind devoting a majority of your hours to studying. You will need to get good grades in college in order to apply for medical school. At the medical school I attended, the average GPA is reported to be 3.85, so even one or two B's can hurt your chances of acceptance.
Aside from this, any major is acceptable as long as you complete the prerequisite courses.
Typical medical school prerequisites include:
Biology: Lecture – 4 semesters; Lab – 1 semester
General Chemistry: Lecture – 2 semesters; Lab – 1 semester
Organic Chemistry: Lecture – 2 semesters; Lab – 1 semester
Biochemistry: Lecture – 1 semester
General Physics: Lecture – 2 semesters; Lab – 1 semester
Math: Statistics – 1 semester
English: Rhetoric (Composition) and Literature – 2 semesters
Medical school takes 4 more years to complete.
After medical school, you are in residency training for 3-6 years depending on your specialty, but you do get paid during those years. (For example, og/gyn is 4 year residency, and general surgery is 5 years.)