Several things:
Age is not an integer - it is a nullable integer type. They are not the same. See the documentation for Nullable<T> on MSDN for details.
?? is the null coalesce operator, not the ternary operator (actually called the conditional operator).
To check if a nullable type has a value use HasValue, or check directly against null:
if(Age.HasValue)
{
// Yay, it does!
}
if(Age == null)
{
// It is null :(
}