Validate Multiple Inputs Together?

[eluser]pistolPete[/eluser]
You could simplify it a bit: You don't need monthCheck(), dayCheck() and yearCheck().

Code:

public function finalAgeValidation()
{
        $month = $this->input->post('ageMonth');
        $day = $this->input->post('ageDay');
        $year = $this->input->post('ageYear');

...
}

Another thought:
Why don't you use a single input field where the date is entered like "01/02/1967"; you could then split the values into day, month and year in a single callback.