John Billington the younger’s wanderings south would have taken him to the nearest native settlement to Plymouth, which is Manomet (about the location of the present Cape Cod Canal). Most of the descriptions I have seen of his wanderings suggest that he walked about 20 miles, which would have put him well past modern Manomet (as well as the Coast Guard station or the now shut down nuclear power plant). He probably had no idea of where he was going, of course, and thus his path would not have been in a straight line. The modern narratives tend to concentrate on his diet, which was minimal, rather than his route, which at this point is unknowable.
Emmanuel Altham, one of the Company of Adventurers for New Plymouth, in his "Letter to Sir Edward Altham" (1623) describes Manomet as the Indian settlement closest to Plymouth. He identifies not the location but the distance: "And now I will speak somewhat of the savages in the country about -- I mean the native Indians. The nearest that any dwell unto [Plymouth] is fourteen miles, and their town is called Manomet." This placemark indicates only a guess of where Manomet might have been
The Manomet location may have been a summer settlement: the natives are known to have moved closer to the coast, and their primary food sources, in the summer, and further inland in the winter. Young John may have been in luck in this timing, because if this had been earlier in the year, there might not have been any inhabitants even that close.