DX Wombat and others should note that there is no weight limit for a JAR PPL or for the SEP rating included within the licence. There is also no limit to the engine power and the requirement for difference training for particular features is a simple mater of getting training from a suitably qualified instructor so that you are sufficiently familiar to operate the aeroplane safely.
The licence allows you to be the pilot of an aeroplane; in the case of a PPL you may not be paid as a pilot (notwithstanding several minor exceptions). The basic Single Piston Landplane rating which most people will have included in their licence at the point of issue allows you to fly the majority of basic single engined aeroplanes and with additional training you can then add a broader range of types.
In theory you could fly an airliner on your PPL but in practice the amount of extra training you would need would be about the same as taking a professional licence and the expense involved would be enormous.
Happy landings
3 point