Different ways of Validating Date of Birth in Model

def validate
if (date_of_birth.month==2 && date_of_birth.month.day > 29)
errors.add(:birthdate, "Invalida date")
end
end

OR

validates_each :date_of_birth do |record, attr, value|
record.errors.add attr, "is not a valid date. You must be at least 18 years old to sign in." if value.blank?
end

OR

def validate
if date_of_birth.month.blank? || date_of_birth.day.blank? || date_of_birth.year.blank?
errors.add_to_base "day, month and year cannot be blank."
end
end