Query-by-example skip primitives?

Yes, you can do it:

Person p = new Person();
p.setLastName("Smith");

Example criteria = Example.create(p).setPropertySelector(
    Example.NotNullOrZeroPropertySelector.INSTANCE
);
List<Person> foundPersons = session.createCriteria(Person.class).add(criteria).list();

Example.NotNullOrZeroPropertySelector.INSTANCE is a property selector that includes only properties that are not null and non-zero (if numeric)

UPD

Above an example for Hibernate org.hibernate.criterion.Example class. For org.springframework.data.domain.Example you can ignore primitive fields by manually specifying names of these fields:

Person p = new Person();
p.setLastName("Smith");

ExampleMatcher matcher = ExampleMatcher.matching().withIgnorePaths("age").withIgnoreNullValues();

Example criteria = Example.of(p, matcher);
List<Person> foundPersons = personRepository.findAll(criteria);