Have you considered getting a Nintendo Switch?
I (37) own both a Switch and a PS4 and generally use the PS4 to play the "grown-up"/online/graphic-heavy games.
On the Switch I play the more "family friendly" ones, which basically are games that remind me of what I used to play as a kid (Zelda, Mario etc.).
9 seems a tad early for a PS4 (but what do I know about kids these days
).
I imagine your son will be a teenager shutting himself off from everyone in front of a screen (e.g. a PS4) soon enough - a Switch is something you could all enjoy together.
And I just checked: Minecraft is also available on the Switch. Though I'm not sure if it has an online mode and if your son would want to play online with his friend. If so, I don't think he could if his friend plays it on a PS4 and your son on a Switch. But that's really the only potential drawback I can see.
The Switch is way more fun, especially as a family console.