The function FLOOR simply rounds down to the nearest integer value. So for example, FLOOR(2.5) will return 2, FLOOR(-2.5) will return -3. In the above case you are using it correctly as a person who is 5.25 is considered 5 years old. One thing though is that the number of leap years which might cause some problems over time. I would suggest dividing by 365.25 to get something a little more accurate.