Double check that the field containing the date is a DATE field ( or a calculation with a DATE as the result )
To expand on Daniele's advice:
Filemaker stores dates as a number of days but displays them in a "date" format. Thus, if the fields are date fields, (not text), sorting them in ascending order should put the oldest dates at the top and the newest at the bottom.
I checked my field and it is a date field however it is still sorting by month, putting all the dates starting 01 together, then 02, etc instead of by the year. Do I need to change how I am entering in dates in order to do this sort. Currently all of my dates are in mm/dd/yy.
If these are date fields, they won't sort as though they are text--which is what you appear to be describing.
How did you check the types? Are they data fields or calculation fields?
I checked my field and it is a date field ...
I do not think so... ( or you are sorting by another field ! )
Try this one:
1) create a new calculated field with this calc:
GetAsNumber( YourDateField )
Which is the result for 11/05/2009 ?