I agree. PPL materials are much simpler and more suitable for beginners. It is also good to take a look at some ppl material just so you will have some general idea what is waithing for you when you start training. You dont need to study anything in advance, the syllabuss is made for pepole with no previous knowledge(except of course basic knowledge in math&physics wich will be tested on entry exam), but it is much easyer to understand classes if you already have some basic big picture in your head.
I personaly went strait to ATPL course nine years after finishing technical high school(so you can imagine that I forgot a lot) and reading manual for MS Flight sim(for playing purposes) and had no problem understanding anything.
Keep in mind that understanding plays only small part in passing exams. Be prepared to
study a lot.
Also search online for free ppl and atpl materials
Hope I helped & good luck with your training!