Citizenship test: When will I be able to apply the N-400 form?

Q: My family and I moved to the United States when I was 20. I’m now 23yrs old, so it’s been for over 3 years. When will I be able to apply for the N-400 form ? Do I need to wait unti l I’m 25. Do I need to have had income tax returns for 5 years ? Because I went to school for last 3 years...