It's really not normal in 6 year olds, no. It's hard to say though whether the toddlers just grew out of it or whether they were taught it's unacceptable. I expect it's a bit of both.
Maybe your patience has extended it or maybe it's helped him feel secure, really - who knows?? Until we can clone kids, no ones ever going to know?!
Obviously you've thought about anything that is linked with it starting again - anything that seems to start it up again?
You said he's speech is fine & he communicates, but does he have the vocabulary and does he know how he feels? I know that sounds odd, but sometimes they need help to decipher if they're angry/frustrated/sad/disappointed and to be able to say why exactly. So it's easier to throw something, lash out at the person asking them to do something.
Say if you ask him to turn off the tv. Does he try to negotiate, or even ask not to until what he's watching is finished? If you say no, we need to leave now. Can he say 'oh that's not fair, I wanted to finish watching this'. (Sorry I'm no script writer 🤪).
If he's not great at this, have you tried saying it for him? 'Are you frustrated because you wanted to finish watching this?'
And use the hideous, but effective, 'DS, use your words!!' 'hitting/kicking is not acceptable'
I don't think you should wait until you mive/he settles because there will
Always be something and he needs to turn that even when life is bloody tough, hitting/kicking is NOT the way to deal with it!
Plus, lots of positive stuff when he's being good. But things like 'DS. That was so kind to share with small DS' or 'DS that's a fabulous Lego creation'. NOT overly praising for just doing as he's told (like turning the TV off) 'Good boy DS, let's go' rather than making a big fuss of it.
Good luck.
He's only little, don't worry about him being a teenage thug 💐