Apex extend standard objects to add business logic

Currently it is not possible to extend a standard or custom object in Salesforce. Why would you want to do that you may ask, think about the following, how would you check the age of a contact, if they have a mobilephone, sort list of objects, serialize, deserialize, .

Contact con = [Select Birthdate from Contact][0];
Integer conAge = con.Birthdate.daysBetween(Date.Today())/365;

if (conAge > 35){
...
}

let's abstract the business logic to isAgeGreater(35) method: cleaner and reusable for any age comparison. 

Contact con = [Select Birthdate from Contact][0];
Obj.IContact icontact = new Obj.IContact(con);
if (icontact.isAgeGreater(35)){
...
}

Define an Obj class that will have inner classes for all the standard objects that needs extra business logic.
1. Constructor for 1 object
2. Constructor for List of objects
3. Methods with business logic getAge, hasMobileNumber, add more if needed.
4. Sorting by any field by assigning SORT_BY
5. Sorting by any direction by assigning SORT_DIRECTION (DESC, ASC)
6. Checking if two objects are equals
7. Serialize object
8. Deserialize object

public class Obj {
     
    public static String NAME_SORT = 'Name';
    public static String EMAIL_SORT = 'Email';
    public static String SORT_BY = NAME_SORT;
    
    public static String SORT_DESC = 'DESC';
    public static String SORT_ASC = 'ASC';
    public static String SORT_DIRECTION = SORT_ASC;
    
    public class IContact implements Comparable{

        private Contact con;
        private List<Contact> cons;
        private List<IContact> conLst;
        
        public IContact(List<Contact> cons){
            this.cons = cons;
            this.conLst = new List<IContact>();
            for (Contact con : cons){
                conLst.add(new IContact(con));
            }
        }
        
        public IContact(Contact con){
            this.con = con;
        }
        
        public Contact getContact(){
            return con;
        }
        
        public Boolean hasMobile(){
            return con.MobilePhone!=null;
        } 
        
        public Integer getAge(){
            return con.Birthdate!=null ? (con.Birthdate.daysBetween(Date.Today())/365) : 0;
        }

        public Boolean isAgeGreater(Integer compareAge){
            Integer contactAge = getAge();
            return contactAge > 0 ? compareAge < contactAge : false;
        }
        
        public List<IContact> getList(){
            return conLst;
        }
        
        public List<IContact> sort(){
           conLst.sort();
           return conLst;
        }

        private Integer sortByName(Contact compare){
            Integer compVal = 0;
             if (compare.Name < con.Name){
                return SORT_DIRECTION.equals(SORT_ASC) ? 1 : -1;
            } else if (con.Name < compare.Name){
                return SORT_DIRECTION.equals(SORT_ASC) ? -1 : 1;
            }
            return compVal;
        }
        
         private Integer sortByEmail(Contact compare){
            Integer compVal = 0;
             if (compare.Email < con.Email){
                return SORT_DIRECTION.equals(SORT_ASC) ? 1 : -1;
            } else if (con.Email < compare.Email){
                return SORT_DIRECTION.equals(SORT_ASC) ? -1 : 1;
            }
            return compVal;
        }
        
        public Integer compareTo(Object obj){
            if (SORT_BY.equals(NAME_SORT)){
                Contact compare = ((IContact)obj).con;
                return sortByName(compare);
            } else if (SORT_BY.equals(EMAIL_SORT)){
                Contact compare = ((IContact)obj).con;
                return sortByEmail(compare);
            }
            return 0;
        } 
        
        public Boolean isEquals(Contact concompare){
            return System.equals(con, concompare);
        }
        
        public Integer getHashCode(){
            return System.hashCode(con);
        }   
        
        public String serialize(){
            return JSON.serialize(this);
        }
        
        public IContact deserialize(String jsonCon){
            return (IContact)JSON.deserialize(jsonCon, IContact.class);
        }
    }   
}

Testing standard object Wrapper

List<Contact> contacts = [Select Id, Name, MobilePhone, Birthdate from Contact];
Obj.SORT_BY = Obj.NAME_SORT;
Obj.SORT_DIRECTION = Obj.SORT_ASC;
List<Obj.IContact> icontacts = new Obj.IContact(contacts).sort();
for (Obj.IContact c : icontacts){
    System.debug(c.hasMobile());
    System.debug(c.getAge());  
    System.debug(c.getHashCode());
    System.debug(c.isEquals(c.getContact()));
}