Conditional Column for Age Range.

I have created a Conditional Column for Age Grouping.

I use  

Age equals null then "Unknown"

Age less than 20 then "Under 20"

Age Less than or equal 29 Then "20-29"

Age Less than or equal 39 Then "30-39"

Age Less than or equal 49 Then "40-49"

Age Less than or equal 59 Then "50-59"

Age is Greater than or equal to 60 Then I want to use 60+ but it keeps putting it to 60 wheh I say ok?

How do I get it to say and use 60+