When i was 9 my sister gave me a laptop she put ubuntu on and it pretty much worked for me. I have a pretty good sense for computers and maths so that probably helped. And on another note, no i didnt get trauma from unrestricted access to the internet because i never searched for stuff like that. The first time I started seeing(and thus avoiding) gore/shock videos was when my classmates also got devices. I think if you teach your kid well they will learn to avoid these things but be carefull because other parents(especially today) dont teach their kids about safety. Your milage may vary, im not a parent.