html table with separated column without outer border

<!DOCTYPE html>
<html lang="en">
<head>
<style>
th, td {
  border: 1px solid black;
}
</style>
</head>
<body>

<table style="width:100%">
  <tr>
    <th>Firstname</th>
    <th>Lastname</th> 
    <th>Age</th>
  </tr>
</table>

</body>
</html>