'RUTH, born Salem, MA say 1686; married Plymouth, MA 2 February 1715/6 (PVR, 91) JOSIAH DUNHAM, born 1694 (Dunham genealogy, 160), son of Eleazer ... and Bathsheba (Whiston) Dunham.'
While this source estimates Ruth's birth year at about 1686, an adjustment of estimated birth years for her siblings puts her birth year later - say 1691. This makes her closer in age to her husband (who was younger than her) and only about 39 (instead of 44) at the birth of her last known child.