How many years will it take to be a police officer?

It depends on the particular department. Many now require a Bachelor's Degree. ---- Although some departments require a degree, most do not. A 4 month full time police academy will do it.
Different agencies have different requirements. In most areas, the requirement is a two year college degree, plus police academy. It is best to check with the individual agency that you are interested in joining to plan for your educational needs.
You have to apply to a Police Academy and most of the time they offered 2 years or 4 years of College in Criminal Justice(most of the time). It all depends of the requirements of your State and how you want to start. If you have 4 years of Criminal Justice in College , you can apply even to FBI and start with better opportunities as police officer and a rank. If you take the minimum ; you will find yourself with work but for further promotions , you have to keep studying at your time and take tests from the Police department and seminars to keep it up. But we need good officers (well prepared); trust me Iam a daugther of a retired agent that made Captain Rank and worked homocide and became the Director Of CI in Puerto Rico. And he did great things and has a bachelor degree in Criminal justice with a minor in Criminal Physcology. Good Luck !!!!