Re: Can this really be that old?
My guess, and it's only a guess, is that it is not completely original. If there were any original in an 1803 cabin/shack left to the elements with no real upkeep, in 2014, I would say it would be very little. That's over 210 years. There would be no roof left, and there is absolutley no way the exterior wood would still be that tight, not to mention all of the "chinking" still in order. The elements are much too harsh. Sometimes, you will still find original Oak type beams in old structures with adz marks, but that's about it for original wood.
My guess, probably built as a repro (look-alike) mid last century, 1940's, 50's, 60's ? That or, HEAVILY refurbished around that time.