I'm assuming since you posted this here you are thinking of a MSN in NP of some type. There are several programs that you can apply to that will take people without nursing experience, but there are a few questions you should probably answer first.
1) What type of NP program do you wish to apply to? This relates to the question of what type of NP do you want to be? Inpatient/Outpatient/Emergency/ICU/Pediatric/Geriatric/Family/Behavioral/Womens. Yes, you can move between inpatient/outpatient with some/all of the NP certificates, but some are more oriented towards one or the other. So, it would be good for you to research the specifics of these degrees and at least determine what population you wish to work with. Also, to have an idea of what part of the healthcare system you wish to work in will help you to identify both the population you like working with and what program is directed towards your interests. In many of my classmates cases, their work as a RN helped them get a better understanding of what their "calling" was, as someone without RN experience hopefully you have some experience in other medical fields and in the medical world to help you to understand what you would like to do and why.
2) Do you feel you understand the environment you will be working in enough to be directing it? I'm not saying in the least that you will not gain any experience or understanding in that environment when you are doing clinicals in your program, but I am saying that I and many of my classmates used our experience as RNs to gain knowledge of how the system works, so that we could have a better understanding of that to build upon while in NP school. We also were able to utilize that base knowledge to build upon when we were in class and in clinical situations. As long as you feel comfortable that you have the base you need to understand and grasp those concepts, then you have the amount of RN experience necessary to be successful in NP school. That may be 20 years, or it may be 0 days, it varies based on the person, the program, etc.
Good Luck finding the program that is right for you, there are many and it takes alot of work and diligence to find the program that is the best fit for your situation.