I suppose it's quite easy for somone who HAS NOT spent 5-6 years in undergraduate education, spent a further 5-7 years (minimum) specialising to slate those that have.
Why don't you try working in a tough environment with ever increasing hours and demands and decreasing resources and then maybe you'll have some idea what your taking about.
In answer to the original question its not that simple (nothing ever is), its not quite like, I think I'll be a plastic surgeon and pop off to specialise, you have to be dedicated and fortunate to end up in the training pathway you really want.
By the way physiotherapy is not a speciality in medicine, doctors are not physiotherapists, physiotherapists are and geriatrics is now known as care of the older adult/elderly