The reason why it takes many years to become a FULLY QUALIFIED priest is because they have to learn the way of life of the priest because of the sacrifices they have made and the commitment they need. They also have to study and learn the whole bible, they are required to earn a Bachelor's Degree and then go to seminary school. This all takes about 5-6 years.(As part of their training they are expected to work alongside a senior priest.)
It can take many years to become an overnight success.
A zen priest must be certified to become a teacher and lead koan study by a properly qualified teacher. Typically, it takes many years of study and practice to become ordained as a priest and many priests are never sanctioned to teach. .
10 to 20 years if you want to be really good
You need a great deal of formal training to become a doctor. You need to train for many years in college and do many clinicals.
Within the United States, it would take four years for the bachelor's degree, and an additional three years of law school.
I would imagine it is a "on the job" training and you would be on probation for a year.
There was no set number of years that a priest could serve as the high priest. He served as long as he lived. See Talmud, Yoma 9a.
A person does not study to become a bishop. They study to become a priest and then work for many years as a priest. If their is a vacancy for a bishop the pope may appoint the person to be a bishop, which Pope Celestine did before he sent Patrick back to be a missionary in Ireland about the year 433.
That depends a lot:* What you want to train for * To what level you want to train
"How many years does it take to become a chemotherapist?"
How many years does it take to become a cytopathologist?
It took her a few months to train for flying.