annotate with @Version:
a) if there is property "version" - annotate it or getter
b) if there is no property "version" - create it and getter/setter and annotate it or getter
c) if there is @MappedSuperclass with "version" - base class for the current class - do not insert "version" into the current class, it should be inserted or exist in the super class;

add a checkbox "Enable optimistic locking" to control this from "Generate Hibernate/JPA annotations" wizard.