I think most of the people who are saying they haven't shaved for years are talking clean shaven. I doubt anyone could leave a beard for long without having to at least tidy it with scissors or a trimmer.
I know loads of people who have ad beards for as long as ive known them, but they still trim them.
My face hates being shaved, goes all itchy, so I usually shave one a week or so. Reduced the irritiation and my stubble grows quite slowly so I can get away with it. There is a day or so in the middle where it gets scratchy before going soft (<2mm) that the GF hates though.
Longest ive gone wihtout shaving, about 3 weeks, but I looked in the mirror one morning and realised I looked like my dad, so off it went!