Check for under age (See related posts)

I would allowing passing in the age as:

def underage?(birthday, age = 18)
  age.years.ago < birthday
end

so you could also use this to see if somebody is under 21 by calling

underage?(user.birthday, 21)

You might also extend Integer like so:

class Integer
  def underage?( birthday )
    self.years.ago < birthday
  end
end

And then do

21.underage?( birthday )

However, I'm using a Date for the birthday and I get

ArgumentError: comparison of Time with Date failed
        from (irb):3:in `<'
        from (irb):3:in `underage?'
        from (irb):6

It seems most logical to use a Date and not a Time for someone's birthday, so there should be some kind of conversion to handle this.

An important note: The Rails ActiveSupport Time Extensions are only approximations of time, so if you're looking for complete accuracy, don't use them. If we're looking for accuracy, then we want to work with date objects.

1.year #=> 31557600 (which is 365.25 days times the number of seconds in a day)

If you're just looking to validate on record creation that a user is old enough, use the following validation:

validates_each :birthdate do |record, attr, value|
  record.errors.add.attr, "You're not old enough." if value > Date.new((Date.today.year - 18),(Date.today.month),(Date.today.day))
end

If you want to calculate a user's age:

def age
  age = Date.today.year - read_attribute(:birthdate).year
  if Date.today.month < read_attribute(:birthdate).month || 
  (Date.today.month == read_attribute(:birthdate).month && read_attribute(:birthdate).day >= Date.today.day)
    age = age - 1
  end
  return age
end

Ah, *great* input.

Thanks guys!