Hmm, there is already a datediff function which will tell you the difference between two dates. And it can return the values in whichever format you like the difference --> in days, months, years etc.. In addition there is no overhead of converting the date datatype to that of an integer.
https://docs.microsoft.com/en-us/sql/t-sql/functions/datediff-transact-sql

When we comparing two columns , it is best to avoid this overhead of conversion.

The function you have created how would it work when you pass the following parameters
DECLARE @DOB DATE = '19991231';
DECLARE @Today DATE = '20010101';

It tells you there are 18870 integers between 31-Dec-1999 and 1-Jan-2001 and divide by 10000=0.18 which means age is less than a year?