I think 4-5 years is a bit much unless it includes junior and senior year research in undergrad, in which case it does sound about right. I would say anywhere over 2-3 years research experience is good. 4-5 years is great but I don't know that it is necessary. From the professors i've spoken to, they seem to want at least 2 years, and are very happy with anything over that. this is of course best if the research is relevant to their work.
My UG advisor told me that the second I declaired psychology as my major if I planned on getting into grad school I should get involved in research at that moment. I was a freshman when I declaired so I had 4 years including summers, and multiple presentations, and co authorships...I think the best advice I have would be at least 2 years of SOLID research not just data entry.