<form name="loginForm" ng-submit="submit()" novalidate>
    <select name="Month" ng-required="true" ng-model="dob.Month">
        <option>1</option>
        <option>2</option>
        <option>3</option>
    </select>

    <select name="Year" ng-required="true" ng-model="dob.Year">
        <option>1</option>
        <option>2</option>
        <option>3</option>
    </select>
</form>

<span ng-if="loginForm.Year.$error.required">This is required!</span>
<span ng-if="loginForm.Month.$error.required">This is required!</span>

<span ng-if="loginForm.$invalid">Month, Year needs to be selected!</span>