I've always outright believed the "Trelane is a Q" fan theory and adopted it as my own head canon. There are too many similarities between both of the characters to ignore. Honestly, one could even argue that they might be the same Q which is a theory I'm starting to enjoy more and more. Who's to say that TNG Q isn't just Trelane all grown up?

The similarities between Trelane and Q are pretty huge which is where the original theory came from but if you start analyzing specific events and comparing them further, there are things to suggest that Trelane was a child but our TNG Q was initially just a teenager. That we've been watching Trelane grow up over the course of the entire series.

Both of them are susceptible to rage when being laughed at, belittled, or ignored and both of them see themselves as Judge of all. Where Trelane started with kindness and hospitality, our Q knows none of it because he's already given it to them as Trelane and seen what they were like. After what must be incalcuable amounts of time to a mortal, Trelane was no longer being punished by his parents. So he set off again with specific vengeance for humanity after what he's seen from the Enterprise crew. Now older and with his powers fully developed, both of material control as well as now nearly full omniscience, he heads to the Enterprise again. Sure, he could alter time and go back and mess with Kirk but he had time to progress. He always gave them a "fair chance" (in his mind) so why wouldn't he this time? See how far Humanity had advanced from the arrogant and backtalking savages that they were, pushing him into a position where he had to be punished by his parents.

So he rocks up on the Enterprise-D. Why introduce himself as Trelane though and start that all over again? Give them a "fair chance", yet again, by saying who he is and what he actually is. No hiding. No illusions. So he toys with them. For the Enterprise crew (and viewers), this Godlike being is just unnecessarily and out of NOWHERE fucking with them. Dragging them around and impeding them just to annoy them. We've never gotten a proper reason as to why Q chose that moment and that time to start screwing with people or why he came with such intense hostility. Sure he uses the "You are too arrogant, pushing into the stars" but... he's God. Humanity, and the Federation, barely know anything about the galaxy their in. He's GOD. He's got the whole universe and timelines he can fuck with but Humanity specifically is really that much of a threat? I mean, a decade later Voyager is about to be flung across the galaxy and struggle like hell to get home. Wouldn't they be a better test of what Humanity is truly like? When pushed into these specific conditions and not just ripped from reality and dropped into a bath like a plaything?

But the more that Trelane/Q fucks with Humanity the more he realizes that he's holding onto that petty grudge. He can't really let it go now though because he's set himself up as this judge and due to all that time focusing on them, and the realization that he might be wrong, he is starting to like these fucking backward apes. One in particular even. A captain who is similar enough to Kirk to bring out that hostility initially but different enough to make Q realize he was wrong. Despite being omniscient, it's almost like Q is realizing and seeing things for the first time in that pilot episode. You can know stuff but ignore that information due to whatever emotional reason. Look at political opinions for more than enough proof of that. Ignoring reality and fact to suit your own needs or to suit a specific narrative that was pre-built. I say that's what Q was doing. He might have known everything about humanity but he didn't care or was ignoring it because he was frustrated that the crew of the original Enterprise fucked with him on Gothos.

That's my headcanon anyway.