Top n Rows in PS Query

Is there any way in PS Query to return only a certain number of rows (for example, 100) after the results are sorted?  I understand how to do this in SQL using ROWNUM, but I am not able to get PS Query to do the ORDER BY prior to the ROWNUM expression criteria. 

The current request is to return only the 100 oldest constituents based on birthdate.  So far I have been unsuccessful in getting PS Query to do this.

Thanks,

Janelle