I'm not completely clear on what you're asking, but it sounds like you just want an approach on how to instantiate your classes and pass them to some methods that can convert their ages.
Without writing all the code for you, here's one approach you could use. Modify it as necessary...
class ConversionQuestion
{
static void Main(string[] args)
{
Human human = ... // create an instance of Human, supply name and age
Doggy doggy = ... // create an instance of Doggy, supply name and age
Console.WriteLine("As a Human, {0} would be {1}", doggy.Name, DogToHumanConversion(doggy.Age));
Console.WriteLine("As a Dog, {0} would be {1}", human.Name, HumanToDogConversion(human.Age));
Console.ReadLine();
}
private int DogToHumanConversion(int dogAge)
{
// convert dog age to human
// return human age
}
private int HumanToDogConversion(int humanAge)
{
// convert human age to dog
// return dog age
}
}