DateControl Events

Hi,
      I have a situation like i need to change the value of a drop down when user changes or adds a value in the datecontrol. In my form i have drop "ddlmonthsofcoverage" and above that i have a datecontrol "birth date". When user enters or changes the birth date i need to check that if he is under 19 years, as soon as user either clicks on the drop down or tab into the drop down from datecontrol. Can any one please tell me how to handle this situation, i don't the events that i need to capture for drop down and datecontrol (new to coding). If possible please send the code in your answer.
 
Thanks in advance, appreciate your help.
GP
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