Все в порядке. Но если вам нужны другие способы без использования строк и столбцов Bootstrap, вы можете настроить таргетинг на конкретную .form-группу в своем CSS. Лично я делаю это, потому что это намного чище, чем иметь много вложенных строк и столбцов. Я бы использовал строки и столбцы только для других целей.
HTML:
<div class="form-group required">
<label class="control-label" for="last"><span class="label label-primary">Last Name:</span></label>
<input type="text" class="form-control" name="frmDemo_last" id="frmDemo_last" placeholder="Enter Last Name" maxlength="50" required>
</div>
<div class="form-group required">
<label class="control-label" for="first"><span class="label label-primary">First Name:</span></label>
<input type="text" class="form-control" name="frmDemo_first" id="frmDemo_first" placeholder="Enter First Name" maxlength="50" required>
</div>
<div class="form-group">
<label class="control-label" for="plan"><span class="label label-primary">Plan:</span></label>
<select class="form-control" name="frmDemo_plan" id="frmDemo_plan">
<option value="">--Choose Plan--</option>
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
</select>
</div>
<div class="form-group">
<label class="control-label" for="plantext"><span class="label label-primary">Plan Text:</span></label>
<input type="text" class="form-control" name="frmDemo_plantext" id="frmDemo_plantext" placeholder="Enter Plan Text" maxlength="50">
</div>
<div class="form-group">
<label class="control-label" for="gender"><span class="label label-primary">Gender:</span></label>
<select class="form-control" name="frmDemo_gender" id="frmDemo_gender" required>
<option value="">--Choose Gender--</option>
<option value="F">Female</option>
<option value="M">Male</option>
</select>
</div>
<div class="form-group">
<label class="control-label" for="gender"><span class="label label-primary">Grade:</span></label>
<select class="form-control" name="frmDemo_grade" id="frmDemo_grade" required>
<option value="">--Choose Grade--</option>
<option value="PK">PK</option>
<option value="00">00</option>
<option value="01">01</option>
<option value="02">02</option>
<option value="03">03</option>
<option value="04">04</option>
<option value="05">05</option>
</select>
</div>
<div class="form-group">
<button type="submit" name="frmDemo_submit" id="frmDemo_submit" class="btn btn-primary">Submit</button>
</div>
<div class="form-group">
<div id="frmDemo_message" class="alert message-submit"></div>
</div>
CSS:
/* I used nth-child(n+number) pseudoclass selector since you wanted to start from the 3rd div with .form-group class to be side by side with each other. */
.form-group:nth-child(n+3) {
width:50%;
float:left;
}
.form-group:nth-child(n+3) input, .form-group:nth-child(n+3) select {
width:95%;
}