The link above have helped me how to calculate difference in two dates, however, I need to do the same on a particular column at run time via MySQL select query inside PHP.
As you said, it's the same table, you could use this query:
SELECT *,TIMESTAMPDIFF(YEAR, DOB, CURDATE()) AS Age FROM Profile WHERE Gender='$gn';
Then you'll find an additional field
age in your result set.