This Condition is on the Personal tab in Search Builder and allows you to find people based on their age. To find those without an age on their record (which means they have no date of birth) use Equal and do not put anything for the Value.

Here are the comparison options:

Exactly that age at that moment
Not that age, but greater
Equal to that age or greater than
Not that age, but less than
Equal to that age and less than
Any age that is not that age

What you use for the Top Group Condition (ALL, ANY, NONE) will obviously change the results, so you need to think carefully about these.

Here are some examples using an age range with the Comparisons staying the same (GreaterEqual 30 and LessEqual 40) and the Condition changing.

Notice the different results:

Comparision: >=30 and <=40

Match ALL
Results are just those age 30-40.
Match ANY
Results are anyone 30 or older as well as anyone 40 and under; excludes the group from 31-39.
Match NONE
No results. There will of course not be anyone who is both 30 or older AND also is 40 or younger.

To exclude one age, add NotEqual 35 as a Condition and you will get everyone from 30-34 and those 36-40.