How to automate the creation of queries in Access?

Firstly, you should not be storing the age in a table - it should be calculated as needed (what happens tomorrow - chances are some of the people will have a birthday)

Anyway, consider using a recordset to get a list of the unique ages, and then using that to create each query. Something like:

Sub sAgeQuery1()
    On Error GoTo E_Handle
    Dim db As DAO.Database
    Dim rsSteer As DAO.Recordset
    Dim qdf As DAO.QueryDef
    Set db = CurrentDb
    Set rsSteer = db.OpenRecordset("SELECT DISTINCT Age FROM tblAge ORDER BY Age ASC;")
    If Not (rsSteer.BOF And rsSteer.EOF) Then
        Do
            Set qdf = db.CreateQueryDef("qryAge" & rsSteer!Age, "SELECT * FROM tblAge WHERE Age=" & rsSteer!Age & " ORDER BY LastName, [Name];")
            rsSteer.MoveNext
        Loop Until rsSteer.EOF
        db.QueryDefs.Refresh
    End If
sExit:
    On Error Resume Next
    Set qdf = Nothing
    rsSteer.Close
    Set rsSteer = Nothing
    Set db = Nothing
    Exit Sub
E_Handle:
    Select Case Err.Number
        Case 3012   '   query already exists
            Resume Next
        Case Else
            MsgBox Err.Description & vbCrLf & vbCrLf & "sAgeQuery1", vbOKOnly + vbCritical, "Error: " & Err.Number
            Resume sExit
    End Select
End Sub

However, this is probably not the way to do it - you have not said why you think you need to create all of these queries. Possibly a better way would be to have just one query, and alter the SQL in the recordset's loop before doing something with the query:

Sub sAgeQuery2()
    On Error GoTo E_Handle
    Dim db As DAO.Database
    Dim rsSteer As DAO.Recordset
    Dim qdf As DAO.QueryDef
    Set db = CurrentDb
    Set rsSteer = db.OpenRecordset("SELECT DISTINCT Age FROM tblAge ORDER By Age ASC;")
    If Not (rsSteer.BOF And rsSteer.EOF) Then
        Set qdf = db.CreateQueryDef("qryAge")
        Do
            qdf.SQL = "SELECT * FROM tblAge WHERE Age=" & rsSteer!Age
'   do something with this query (export as an excel/csv file perhaps)
            rsSteer.MoveNext
        Loop Until rsSteer.EOF
    End If
sExit:
    On Error Resume Next
    rsSteer.Close
    Set rsSteer = Nothing
    DoCmd.DeleteObject acQuery, "qryAge"
    Set qdf = Nothing
    Set db = Nothing
    Exit Sub
E_Handle:
    MsgBox Err.Description & vbCrLf & vbCrLf & "sAgeQuery2", vbOKOnly + vbCritical, "Error: " & Err.Number
    Resume sExit
End Sub