If you just sort the column "ascending" or "descending," you will get, say,
January 1950 to December 1975, which won't help you. Here's what I do: set
up a second column next to the birth dates. Format the column to indicate
the month only; mmm or mm will do this. If the dates start in cell C2, enter
in D2 the formula "=C2" and spread this formula down to all the dates. Each
entry in column D will show Jan, Feb, Mar, or 01, 02, 03, etc.
Then, insert the title "Mo" in D1, sort the whole list by the "Mo" column,
and you will isolate all the people born in each month, regardless of year.