Let’s agree that President Trump is a bully and a blowhard and that his tweet mocking Greta Thunberg, the teenage Swedish climate activist, was tacky and mean-spirited. On Thursday morning Trump tweeted this about Thunberg, Time magazine’s “Person of the Year”: "So ridiculous. Greta must work on her Anger Management problem, then go to a good old fashioned movie with a friend! Chill Greta, Chill!”

Within a few hours Thunberg changed her Twitter bio to read: “A teenager working on her anger management problem. Currently chilling and watching a good old fashioned movie with a friend.”

Trump had it coming for his petty put-down, which wasn’t the first time he mocked Thunberg. But some commentators on Twitter seemed to think that any criticism of her was out of bounds because of her tender age. Some contrasted Trump’s tweet about Thunberg to Melania Trump’s complaint that a witness at the House impeachment hearings who mentioned Barron Trump had invaded the privacy of a “minor child.”

There were also suggestions that Trump was targeting Thunberg because of her Asperger’s diagnosis. I suspect that Trump would have told any teenager who sternly lectured her elders on climate change to relax — especially if that teenager was Time’s Person of the Year.

Trump aside, a teenage activist who cultivates publicity — granted, in a noble cause — should be prepared for criticism.

Thunberg, unlike Barron Trump, is a public figure. Indeed, she has become a kind of secular saint because of her activism. In doing so, she has called attention to her youth, inspiring predictable punditry about a “children’s crusade.” In her speech at the United Nations Climate Action Summit, she told superannuated policymakers that “you have stolen my dreams and my childhood with your empty words.” (It was the ultimate “OK boomer.”)

Some of the criticism of Thunberg, such as Trump’s trolling, has been petty and some has been downright offensive, such as a Fox News guest’s description of Thunberg as a “mentally ill Swedish child.” But giving Thunberg a blanket exception to criticism because she’s “only a kid” is just as patronizing as dismissing her arguments because of her youth.

Michael McGough is the Los Angeles Times’ senior editorial writer, based in Washington, D.C.