Click on the Title text entry box and type Age Entry. This message will appear as soon as the clerk points to the entry cell. You can omit this step if you feel that it is not necessary to provide the instructions by unchecking the checkbox. There you can type a warning if an entry error has occurred. The instructions of what is desired can be repeated at that point.
Data validation is very powerful.
You can specify date ranges or even calculate acceptable results based on data entered in previous cells. It is worthwhile to take a look at the help associated with this command. In your case, it will save you a great deal of grief. Internet Sometimes I am completely unable to copy text from a page on the Internet. Other times, a Print command will take care of it.