Multi level sorting for single filed in xsl in asp

Question

I am using stored procedure to retrieve xml so this xml data showing in grid using xsl, from sp i am getting two fields sortorderage and age here sortorderage contains bit values if age is there or not and age filed have actual age so based on this two fields we will sort the grid here i am able to sort asc and desc but my requirement is always show null values in down side upper side show only values that is age and sort those upper values and bottom always show null values using  sortorderage bit 1 or 0 i implemented this in vb script and xsl so here how should i do multi level sort for single filed in xsl.