Ahh, sorry. Just forgot the tabindex. After you make the changes in the Register.template.php, do this:
Find:
<input type="password" name="passwrd2" size="30" tabindex="', $context['tabindex']++, '" />
</td>
</tr><tr>
<td width="40%">
<b>', $txt[563], ':</b>
<div class="smalltext">', $txt[566], ' - ', $txt[564], ' - ', $txt[565], '</div>
</td>
<td>
<input type="text" name="bday3" size="4" maxlength="4" value="" /> -
<input type="text" name="bday1" size="2" maxlength="2" value="" /> -
<input type="text" name="bday2" size="2" maxlength="2" value="" />
</td>
</tr>';
Replace:
<input type="password" name="passwrd2" size="30" tabindex="', $context['tabindex']++, '" />
</td>
</tr><tr>
<td width="40%">
<b>', $txt[563], ':</b>
<div class="smalltext">', $txt[566], ' - ', $txt[564], ' - ', $txt[565], '</div>
</td>
<td>
<input type="text" name="bday3" size="4" maxlength="4" value="" tabindex="', $context['tabindex']++, '" /> -
<input type="text" name="bday1" size="2" maxlength="2" value="" tabindex="', $context['tabindex']++, '" /> -
<input type="text" name="bday2" size="2" maxlength="2" value="" tabindex="', $context['tabindex']++, '" />
</td>
</tr>';
Fixed the message above too.
What about forcing the users to enter their age, have you tried that?