In the United States medical school is traditionally 4 years, and occurs after getting an undergraduate degree (which also usually takes 4 years). In this system, the youngest someone can be (if they didn’t skip any years of schooling) by the time they earn their medical degree is about 25. This means that if someone goes directly from college to medical school, they won’t have had a true paid job until the start of residency.
There are certainly many benefits to this system. Being a doctor takes a certain level of maturity and responsibility. It can be argued that someone who is older, is therefore more capable of handing the weight of being a doctor. Also the additional years of training can lead to better training.
However, there is also the argument that an undergraduate degree does not really help with medical school. There are some basic science classes that are helpful stepping stones for the more complex science taught in medical school, but generally all the other classes taken during undergrad are not directly useful for learning medicine.
If all the required basic science courses of undergrad were compressed into one year, the entirety of medical education could take 6 years instead of the traditional 8. There are some programs in America that currently do this, however they are few and far between.
In several other countries, this six (or sometimes 7) year structure is the norm. Some countries even treat medical school almost like a trade school – students can be accepted straight from high school or earlier, and the remainder of their schooling is dedicated to medicine alone.
When there are so many different systems and different ways of teaching it is hard to definitively say that one works better than another. However, knowledge of different systems is certainly important in continuing to modify and improve our own current system.