How to use datediff to get age less than 12 months

Question

Dear Partners in coding,

 

I want to appreciate all your support and tips you have been giving me so far.

 

I have this challenge  i want to get all the age of my patients under 12 months, i tried using Datediff(mm,DOB,Getdate()) this did not give me the age when i compare with the documented hard copy.

 

please i will appreciate any fast solution to this issue.

 

thank you