I think it's pretty common for bright kids to not really care about school very much (anecdotally, especially boys!). My brother is a similar age, he's in year 8 right now, and I think he stays engaged at school by competing with his friends for the top marks!
I guess, to some extent also, it's really easy to see school as trivial because what you're learning isn't really put in perspective. Like, in maths for instance, you might be taught all of these concepts so that you can do all the problems in your textbook, but at the time you're never told about how useful maths is for developing problem-solving skills and logical thinking, which are actually really important things.
But, to answer your question, starting tutoring now, if your son would enjoy it, isn't a bad idea. He needs to be engaged though, otherwise it's a waste of time and money, I think. But there are also a bunch of other ways to learn things without getting ahead academically. Music and art lessons as well as hobbies generally are shown to be very good for the brain, especially if the kid enjoys it and can focus on it. Even something like after school/weekend language courses could be useful.
I don't think it's too early to start extending, really. But it's also something that he should want to do. Also, it's worth talking to his teachers too. When I was in about year 8 I was really bored with everything, so my mum spoke to some teachers and they would do certain things, like mark me more harshly, or even suggest different assignments to do. My English teachers were especially good at suggesting books to read. Also, some schools give bright students some time out from class to work on whatever the kid is academically interested in with a teacher, it's worth investigating if his school has a programme like that, because they're usually really good.