But not all 7yo are like that. Neither of mine would have been.
Without a parent there to rein him in my DS1 would definitely tell everyone round him his whole life story, whether they wanted to hear it or not!
He would probably make a right song and dance about any food as well - he drops/spills everything!
He is also the biggest fidgeter - I can't even cope with sitting on the same sofa as him.
And lord help anyone near him if his brother was in the vicinity, the fighting, arguing, winding each other up would be unbearable.
My youngest would be terrified and probably cry for the whole flight if not next to a family member.
I would never expect another passenger to look after them. But just being sat next to them and ignoring them still isn't going to mean that passenger has a pleasant flight!
Obviously, I would book and pay for us to have seats together, but I think it stupid of airlines not to sit children with a parent as standard. It would be bloody awful for the other passengers and that's without the safety aspect of what would happen in the event of an emergency (my DS1 also has allergies so there's the risk of anaphylaxis to throw into the mix. And my DS2 gets travel sick!)