The International Genealogical Index has various 'submitted' listings for children of Thomas R Gordon and Isabelle Porter
John, born 1760 in Aberdeen
Thomas R, born 1766 in Aberdeen
Samuel, born 1770 in County Down
William, born 1773 in County Down
James, born about 1775 in County Down
Jane, born about 1777 in County Down
Not surprisingly, there are no matching listings in the OPR index or the RC index at Scotland's People. This suggests that no record of any of these children has survived in Scotland. Nor are there any matching marriages in the OPR or RC indexes (barring weird spellings of either surname).
The first listed child was born in 1760. Therefore Thomas R senior's birth date is a guesstimate based on the assumption that he was aged 25 when his first child was born. This assumption has its uses, but it cannot be relied upon to be an accurate indication of the date of birth.
The IGI also says that Thomas R junior died on 12 October 1841 in Warren, Trumbull [County], Ohio, USA and William died on 20 January 1841 in Brown Township, Ripley [County], Indiana, USA
It looks to me as if someone who has done some work on this family has submitted the information to the IGI. If you want to unravel this lot you need to go back and find out where the information in the IGI came from. It could be a family bible, or some other unpublished source. The IGI unhelpfully says, 'No source information exists', but it has to have come from somewhere.