DT = (From row In DT.AsEnumerable()
Group row By key = row("Age").ToString() Into Group
From firstRow In If(key = "N.A", Group, Group.Take(1))
Select firstRow).CopyToDataTable()
->Group row By key = row(“Age”).ToString() Into Group
This groups the rows by the value in the Age column
->From firstRow In If(key = “N.A”, Group, Group.Take(1))
If the key(Age) is “N.A”, it takes all rows in that group.
If the key(Age) is anything else, it takes only the first row of the group (Group.Take(1)).