Not really a specialist or anything, but I surmised that aging creates what you could call "bad chemicals" in your body.

> unavoidable byproducts of enzyme function, for example, or of protein-to-protein interactions, errors in DNA transcription or translation.

One would surmise that aging adds "bad chemicals" to your body at some set rate. If you ALSO eat old things, that are already full of these "bad chemicals", your body will acquire these bad chemicals faster (because of the extra source).

In short, this research shows that there is some byproduct of the aging process that can be transferred from one organism to another and cause aging in the second organism.