I don't think I have ever had a cleaner shrimp live more than two years tops, if even that. Peppermint shrimp I don't think I have ever kept for more that a year, don't know if something eats them or what, but I don't stock shrimp eating fish.
Don't know if I am doing something wrong, they just eventually disappear. I've got some old fish too, so it's not that I have a death tank or something.