I am a half-elf predator at lvl 11. My understanding is that I can wear medium armour at some stage. Is this correct and, if so, does anyone know what level this is available at?
Yes you will be able to use medium armor. As an example of what you have to look forward to, Pristine Carbonite Breastplate is somewhere around 162 AC, with additional stats and resists.
My lvl 21 Swashbuckler currently has an AC of almost 900 and resists of over 200 in all categories. Note: I am not tricked out by any means.