You are starting your PPL and we all absorb knowledge at a different rate so any comment by definition is a generalisation, however I am not convinced for the "average" pilot you are ready to start aeros at the end of your PPL or even during your PPL. Why? Well the PPL for most is fairly challenging and you are unlikely to end it being fully comfortable and confident with the aircraft throughout its flight envelope. If you are not comfortable (and a good aerobatic instructor will tell you pretty quickly if he is honest) gain a few more hours ( maybe somewhere around 100 in total) and then start aeros seriously. If you are the "average" pilot you will find you progress far more quickly and your money is better spent. Again, I am refering to the "average" pilot. Of course the younger you are inevitably the quicker you may learn and of course some take to flying so much more readily than others!