How to check whether a checkbox is checked in jQuery?

I need to check the checked property of a checkbox and perform an action based on the checked property using jQuery.

For example, if the age checkbox is checked, then I need to show a textbox to enter age, else hide the textbox.

But the following code returns false by default:

if ($('#isAgeSelected').attr('checked'))
<script src=""></script>

<input type="checkbox" id="isAgeSelected"/>

<div id="txtAge" style="display:none">
Age is selected

How do I successfully query the checked property?