You realize, of course, that it is virtually impossible to date a door from a photo! Ledged doors like this have been made for hundreds of years to much the same design and that continues today. A couple of things to note in yours are (1) the ledges have been nailed rather than screwed and the nails seem to be clenched over, this is the traditional way of doing it and these days only really expensive doors are made that way (like Jack Badger's, for instance). (2) The beading on the front is popular these days (hard to find new plank doors without this style of bead), but I believe it first became popular in the late 18th - early 19th century. (3) The strips covering the joints on the rear look to be later additions, but they obscure the joint. Earlier doors were lap or butt jointed, later doors are tongue and grooved.
Overall, if the above impressions are correct, the planks are lap-jointed and it's been stripped of paint (like it looks to have been), then it could be as old as late 18th century, but equally it could be later copy (impossible to know for sure). If it's tongue and groove jointed, then it's probably later, possibly as recent as mid/late 20th century.