I don't think age can be a deterrent factor in HR Jobs. It would rather indicate a person's sensibilities and experience. Physical appearance is also not any indicator of a good HR Person. But yes, ideally its expected from them to be smart, energetic and having good interpersonal skills.
Hierarchy depends on organizational structures. It could be following for example-
HR Coordinator>HR Executive> Assistant Manager>Manager>Sr. Manager> Assistant Vice President> VP-HR
In my opinion in some industries like retail, marketing, finance and service industries they prefer good looking persons and young professionals. Appearance should not matter but some service industries giving preference to pleasing personality and good looking persons.
Hierarchy of designations depends upon the organization.
But general structure can be: Associate / Assistant / Jr. Officer - Executive / Officer - Sr. Executive / Sr. Officer - Asst. Manager - Dy. Manager - Sr. Manager - AGM /Dy. GM -General Manager - AVP-VP-Sr.VP - Director
So it will be wrong to say that such external factors don't matter. Generally also, good looking people attract more attention than the rest.
In my view :-
There is no denying the fact that gender and appearance does play a role in the selection process of the candidate. As far as influence of appearance and gender in HR is concern it is more to do with the organisation policy, average age/population of the organisation and the mindset of the recruiting person. A younger organisation like call centers would prefer a younger and smart HR professional whereas a more mature organisation like a manufacturing set-up would prefer a middle aged person. In a long run it is only the quality of the candidate that will determine the growth of a professional.
On the aspect of structure or hierarchy , there is no defined hierarchy. The hierarchy will be based on the type of the organisation and the strength (headcount) of the organisation. For example if the organisation is a manufacturing setup with maybe 100 odd employees then there would not be chain of HR members , maybe an assistant and a manager who would be reporting to Operations head. On the other hand if it is a service industry with a similar headcount then you may have 4/5 people in HR at various levels of Hierarchy.