hi evan,
i think you forgot the create the pdata fields you are trying to alter.
you need pdata-add. pdata-copy create "p0" for you automatically, but
"p-end" and "age" are not created.
(with-primitive stuff
(pdata-add "p-end" "v")
(pdata-add "age" "f")
(init-particles (pdata-size))
(pdata-copy "p" "p0"))
hope this helps,
gabor