Check whether all checkboxes are checked and then execute a function
I was thinking something along these lines. The condition checks whether there are no unchecked checkboxes (length of the selection is 0) and then executes the appropriate branch.

$("#btnSubmitToCheckOut").click(function(event) {
    if ($('.age_agree input[type="checkbox"]').not(':checked').length == 0) {
        $(this).parents('form').submit();
    } else {
        alert('Please accept all the Terms and Conditions');
    }
});