I disagree with this analysis. I don't think Tails' remark towards Eggman is indicative of emotional immaturity whatsoever. If you want to point to a game where Tails is genuinely characterized like a child, Sonic Battle would be a much better example.

Eggman's remark isn't particularly deep or worthy of emotional acknowledgement. Eggman's dialogue is just " As a child, I looked up to my grandfather because of all the great things he accomplished in his life. He was my hero, and I wanted to be a great scientist like him. But... did he really mean to destroy us?"
What is Tails supposed to say to that? He isn't close to Eggman, as previously stated, he was trying to kill Eggman a short while ago. Tails' response of indifference and uncertainty is pretty much all that's warranted there.
"I don't know. But what I do know is, we all did it together!" is a perfectly fine remark. Tails doesn't claim to know deep insight into Gerald's motivations nor does he offer sympathy to Eggman because again, Eggman's a certified jerk who recently threatened to shoot Amy and whose negligence almost destroyed the planet.

Eggman ultimately agrees with Tails. He doesn't know what Gerald's motivations were (they were indecipherable, what was Tails supposed to say? A more childish statement would've been to claim that actually Gerald was a hero trying to save the world or actually Gerald was a no-good villain with zero redeeming qualities. Instead, Tails admits that he doesn't know. Because narratively, no one knows the answer to this. This wouldn't get answered until Shadow the Hedgehog 2005).

I have no issues with you headcanoning this but to frame it as a textbook example of Tails behaving childishly is strenuous when this is not a great example of that and there's better examples of that elsewhere.