sql group update column by age range

I want to update the class column of 33-year-olds as 2, 34-35-year-olds class column as 3, 36-year-olds class column as 4. I’m using Microsoft SQL Server.

ID DATE_OF_BIRTH CLASS
1  10.10.1986    1
2  11.02.1987    2
2  18.04.1988    3
.....................
.....................
.....................