Not Able to Select Value Of Combo Box Using Key

Hi

I am doing a web application in that i have a combo box

<SELECT class="TextBoxNormaL" id="_ctl5_CboAge1" name="_ctl5:CboAge1">
<OPTION value="0" selected></OPTION>
<OPTION value="1">0-7</OPTION>
<OPTION value="2">7-14</OPTION>
<OPTION value="3">14 above</OPTION>
</SELECT>

But I am not able to select this combo box value to diff valuse pressing 0,1 or 7...

Thanks