Like all kids, he probably read the pulp mags. Jules Verne, ER Burroughs and HG Wells were pretty popular at the time, I'm sure it was something he wouldnt have been able to avoid (like STAR WARS), I'm sure he probably enjoyed it.
When he was getting into writing, SciFi was just capping off the Silver Age and going into the New Wave stuff (which he partially influenced). What that means is you had cheap, well-written, trippy books in drugstores, bus stops, newspaper stands, etc. They were everywhere -- to the point of being mundane. They were just something to kill time in a coffee shop or whatever.
Anyway, that's how I picture him, more of a dabbler, picking up bits by happenstance. Not a hard core fan who would follow any specific SciFi writer, nor have a subscription to ASTOUNDING TALES.
Science Fiction came to him. I dont think he went to it.