I have 3 in my 16 I've had for the past 1.5 years, I'd say maybe 3-5 years is average?
My tanks (so far
5.5 gallon Planted Dwarf Puffer tank (2 Dwarf Puffers and a lot of RCS!)
16 Gallon Planted
(GBR pair, 3 amano shrimp and a whole bunch of snails!)