Length of experience will help an interviewer determine what strengths you may have and what area your skills may be most well utilized. Rather than just giving a specific amount of time, also share what your primary responsibilities were during that time.
"I have been a nursing aide for X years. The majority of my experience as a nursing aide has been working in long-term care facilities. I do have some experience working as a home health nursing aide, as well."
"I just recently became certified as a nursing assistant. I love caring for others and am really looking forward to the experience of being a nursing aide."
"I have been a nursing aide for X years. I initially began my medical career as a medical secretary. While I did enjoy that work, I really wanted to find something that allowed me to have a more hands-on role with patients. I really enjoy being able to be actively involved with the care of others."