Below is an image of the primary source [1] first placing John Wetherby I in Massachusetts, and also establishing his birth year as 1641 or 1642.
On 2 • 8 • 66 (2 Oct 1666), John Wetherby testifies in the Court of Middlesex County, Massachusetts, in the case of William Kerley vs. Thomas Rice & others. Wetherby (or Wetherbee) is spelled Witherbee in the transcript. October is the eighth month in the Julian calendar used in England and the British Colonies at the time.
In his testimony, John Wetherby states that he is “aged about 24 years,” so it is likely his birth date is before 2 Oct 1642, in either 1641 or 1642.
William Kerley is the Constable of Marlborough, Massachusetts. He files a complaint against Thomas Rice, Edward Rice, and Joseph Rice (three brothers), and Peter Bent claiming they failed to perform night watch duties for the town.
Apparently, John Wetherby was performing night watch one night with Thomas Rice, and John testifies about their encounter with the Constable, John Barnes, and Nathanial Johnson during that watch.
Although the events occur in Marlborough, it is interesting to note that most of the involved parties probably knew each other in Sudbury, Massachusetts, where most of them lived previously. Among the early settlers of Sudbury, we find William Kerley, Edmund Rice (father of Thomas, Edward, and Joseph), John Bent (grandfather of Peter Bent), and Solomon Johnson (possibly related to Nathaniel).
Note below the interesting coincidence regarding John Wetherby and Thomas Rice.
John Wetherby (1642-1711) is 9th great-grandfather of MKS in the Wetherbee branch.
Thomas Rice (1625-1681) is 10th great-grandfather of MKS in the Watne branch.
References:
[1] FamilySearch; Colonial county court papers, 1648-1798; Folio 40; Middlesex County (Massachusetts), Clerk of Court; Family History Library Film 901001 / DGS 007902664.