How to sort column by date in Numbers?
Your dates might not be recognized as dates by Numbers. 

In my case, Numbers does not offer dd/mm/yyyy as one of the standard date format and I have to define a custom format for that pattern. (Not sure, if that applies in your case: The date must be entered according to your locale settings - I can set "dd/mm/yyyy" as the date format, but I have to enter it as "dd.mm.yyyy" on my German system.)

Using the sort &amp; filter window then works well on the formatted dates.