Please see the code below:

public class Person {    public DateTime DateOfBirth;    public List<Offer> Offers = new List<Offer>();    public Person(DateTime DateOfBirth)    {         int age = DateTime.Now.Year-candidate.Year;         if (DateTime.Now < candidate.AddYears(age)) age--;             if (age < 18 || age > 99)                 throw new ArgumentException("Age must be greater than 18.", "DateOfBirth");     _dateOfBirth=dateOfBirth;    }     public void GetOffers(IOfferCalculator offerCalculator)    {      return offerCalculator.GetOffers(this);    }     public void AssignOffers(List<Offer> offers)    {       //Assign offers to Person.Offers here.    } } 

Notice that I pass the entire Person object to Person.GetOffers(). The reason I do this is because the person has to be over 21 for all of the offers and this is checked (validated) in the Person constructor. Is this a good reason to pass the Enquiry as an object to: offerCalculator.GetOffers? The reason I ask is because t3chb0t described this as a code smell in my question here: https://codereview.stackexchange.com/questions/186124/testing-the-process-of-assigning-offers-to-a-customer

Alternatively I could just pass the DateOfBirth like this: return offerCalculator.GetOffers(DateOfBirth). However, this would mean that I would have to validate the DateOfBirth in every offer.

I am trying to follow the principle of least astonishment these days and find myself overthinking a lot. My two questions are:

1) Is it a good appraoch to pass the Person object to offerCalculator.GetOffers as Person already validated the date of birth?

2) Should I be checking the date of birth against every Offer, even though every Offer requires the person to be over 21? I don’t think this will evert change i.e. the person will always have to be over 21.