I think it depends on how responsible my son is when he get older. He is great at 5 when he is on youtube and we tell him that's not appropriate to please change it he listens. So if he continues and is still very big into sports and activitys then middle school but things change and each kid is different.
My daughter has one now but I was passed down to her and isn’t activated. She likes it better then a tablet some complains tablets are to big. She won’t be getting an activated one til 12 or 13 unless she gets more involved with dance and I have to leave her and come back. However, she is buttering her dad up to agree to 10 instead of 12 and he’s jelly when it comes to her lol.