I read the PD forum quite a bit (and not just because I am a moderator )

There are some very intelligent, informed people there who post lots of scientific studies about the blood brain barrier, genes, mitochondrial damage, toxins, statins, you name it. There is a gene called the Parkin gene.

They do mention young onset PD... Micheal J. Fox has this type.

But like most neurological problems, there is not one answer for all PD patients.

We are seeing younger patients and many of them male on Myasthenia gravis forum (+50 used to be the stated onset for MG in males), and here, we see more young people every day.

I think vaccines may play a part. Diet, and toxins, too. At least here we do see RX drugs as triggers fairly often.
They may combine, and be synergistic. And the triggers may only work in certain genetic combinations with people who have a weakness of some type.

More and more people are deficient in certain nutrients due to RX drug depletions, or poor diet. 40% B12, 70% magnesium,
70% low Vit D, are recent discoveries. B12 and minerals are affected greatly by the acid blocking drug use OTC and RX.

So understanding how our bodies work, and how to take care of them, is a major educational point of view at least for me to provide here. And it seems I say the same stuff over and over and over!