You could use a
wildcard Find/Replace, with
Find = <[MTWFS][ondayueshrit]{2,7} [JFMASOND][anuryebchpilgstmov]{2,8} [0-9]{1,2} [0-9]{2,4}*^13
Replace = ^&
setting the replacement font to 14pt bold.
This will capture the dates regardless of whether the days & months are abbreviated or written out in full and whether the years are 2-digit or 4-digit.
If there is anything else on the line before the date, change the '<' at the start of the Find expression to '[!^13]@'
No macro required.
As a macro, it becomes:
Code:
Sub Demo()
Application.ScreenUpdating = False
With ActiveDocument.Range.Find
.ClearFormatting
.Replacement.ClearFormatting
.Replacement.Font.Bold = True
.Replacement.Font.Size = 14
.Execute FindText:="<[MTWFS][ondayueshrit]{2,7} [JFMASOND][anuryebchpilgstmov]{2,8} [0-9]{1,2} [0-9]{2,4}*^13", _
ReplaceWith:="^&", MatchWildcards:=True, Forward:=True, Format:=True, Wrap:=wdFindContinue, Replace:=wdReplaceAll
End With
Application.ScreenUpdating = True
End Sub