I don't see why not, men sometimes do get non cosmetic tattoos on their penises, cosmetic tattoos should be no different.
Nothinghere- when you get your eyebrows tattooed the needle isn't put as deeply into the skin as a non cosmetic tattoo; so 3 years sounds about right. For conventional tattoos they do need to get touched up every couple of years; dependant on amount of sun exposure, if the ink was high quality how expert the tattoo artist was with the needle (amateur tattooists either put the needle too deep into the skin causing 'blow outs' meaning the ink spreads underneath the skin making the lines look too thick and splotchy or they don't put the needle in deep enough causing the ink to fall out) and the colour of the tattoo. You'll notice more so if a tattoo in colour has faded rather than a tattoo in all black.