The birth age range for John is an estimate taken from Anderson (TAG, 61:22).
John Bland was a proprietor and farmer in Watertown, MA, in 1636. He became one of the earliest settlers of Martha's Vineyard, having owned land there as early as 1646 where he was associated with the Mayhews in the first movement from Watertown to Martha's Vineyard. He frequently called himself John Smith, this even prior to arrival in New England. Probate records include the John Smith name.
From the GDMNH, p. 95, 96): "John Bland, alias Smith, was living at Edgerton on Martha's Vineyard in 1646, undoubtedly the John Smith associated with the Mayhews in the first movement from Watertown to the Island, where he was always Bland. In Watertown lived his mother Adrian, 2d widow of Jeremiah Norcross and there is recorded Isabel, wife of John Smith, bur. 12 July 1639, age 60. The Hampton Drakes attest that they knew his daughter, Isabel Bland, from childhood, that her father, John Bland lived in Colchester and that his ancestry was Bland, not Smith. Apparently his stepfather was Smith. His will made 2 Nov 1663 names " wife Joanna and all the children that are alive that I owne: Isabel m. 1st Francis Austin, 2nd Thomas Leavitt; Annabel m. William Barsham of Watertown, eldest son of John."
The Littleton, MA VRs state that several male Smiths "perhaps" or "probably" are the sons of John.