Major Section 15.2.6 The edm:FunctionReference Expression states that its value is a reference to the return type of a function. This seems to be a leftover from removing model functions.
The example uses Function="org.example.person.GetAge", which indicates that it points to a model function as it uses the same prefix as the org.example.person.Age value term, which implies that GetAge is defined in a schema (as a model function would have been) and not in an entity container (as a function import must be).
Also the introduction of Type Definitions now allows giving a name to primitive types with facets, so even primitive return types with facets can now be given a name, reducing the need for referring to implicitly defined types.
The meaning of a ParameterReference as defined in section 15.2.12 is unclear, and the example gives no hints on how to interpret it,