I was like this as a child, and I now have sentimental DS10 who weeps if you throw things out. I view the hoarding impulse as an anxiety behavior.

We have "throwing out" practice, actually, where we make choices together about what to keep and how to store what is kept. It has to be in his room (not mine...), and it can't be spread all over the floor. This takes a lot of 1:1 coaching and support, but has gotten better over time.

DeeDee