If you want to change the Age interval then mark the group Age at first service by clicking on it and press the button Options.
You can now change the intervals to the values you prefer and press the Tab key on your keyboard to move to the next box or click with your mouse. Press the OK button and it will be saved in the layout.
Note: If you want to save this change permanently you need to make your own copy of the layout. See: How to set up and use layouts.