The psychologist Steven Pinker was once quoted as saying that the best way to tell if someone was under 30 was if they were comfortable using "fun" as an adjective.

About 15 years later, that still seems on target. The farther away in the rear-view mirror 45 is for you, the odder it seems to hear something like "his party was funner than hers." And the younger you are, the more it seems perfectly normal.

In my new e-book, You Need to Read This: The Death of the Imperative Mode, the Rise of American Glottal Stop, the Bizarre Popularity of "Amongst," and Other Cuckoo Things That Have Happened to the English Language, I write about fun-as-adjective and a number of other trends that young people have brought into the language.

Note that I call these "trends," as opposed to "horrible crimes against English." I know that some people decry new word-meanings and usages, while others defend them. My purpose here isn't to engage in that argument but rather to chart the course of change.

To that end, I thought it would be fun to come up with a Pinker-like watershed age for some of these developments. Instead of just guessing, I devised a survey and sent it out via social media. First, I asked people to put themselves into an age range (18-25, 26-35, 36-45, etc.), and then, for each point of usage, I asked whether they themselves spoke and wrote that way.

Now of course, given the number of English speakers in the U.S., not to mention the world, the results aren't scientific. And some people probably reported being more "proper" than they actually are. Finally, there are clearly factors other than age at work here, most obviously education. But the results are still pretty instructive.

In each case, I give the traditional usage, the more recent one, and a Pinker point — meaning that the majority of people younger than that age use the new version while the majority of people older than that the traditional one.

1. Fun as adjective

Old school: "That would be a lot of fun."

New school: "That would be very fun."

Pinker point: 55

Note: This actually jibes with Pinker's original observation. That is, in the time since he made it, a somewhat older group has become comfortable with the usage.

2. Singular "they"

Old school: "Everyone who wants to come on the trip should bring his or her ticket."

New school: "Everyone who wants to come on the trip should bring their ticket."

Pinker point: 65

Note: This usage is very common in speech, British published texts, and online writing. (I used it myself in the introduction of this article, when I wrote you could "tell if someone was under 30 was if they were comfortable" with "fun.") But it hasn't yet penetrated to standard American sources like The New York Times, The New Yorker, and major publishing houses.

3. "Big of"

Old school: "It's not too big a deal."

New school: "It's not too big of a deal."

Pinker point: 25

4. "However" as conjunction

Old school: "It rained yesterday. However, tomorrow looks nice."

New school: "It rained yesterday, however tomorrow looks nice."

Pinker point: 25.

Note: This usage is frowned on by those ages 26 to 45, but picks up popularity with the 46-and-older crowd, and is also extremely popular among my college students. Clearly, more research is needed.

5. "Lead" as past tense of "to lead"

Old school: "The general led the troops into battle."

New school: "The general lead the troops into battle."

Pinker point: 25

Note: This is another one used by a sizable majority of my students.

6. "Mic" as the abbreviation for "microphone"

Old school: "He picked up the mike and started to sing."

New school: "He picked up the mic and started to sing."

Pinker point: 45

Note: I explored the history of this change in abbreviation here.

7. Present-tense "lay down"

Old school: "After lunch, I like to lie down and have a nap."

New school: "After lunch I like to lay down and have a nap."

Pinker point: 25

Note: The singer-songwriter Sufjan Stevens wrote Miley Cyrus an open letter criticizing her for making this mistake in her song "#GetItRight," which includes the line, "I been layin' in this bed all night along." He was a little obnoxious to correct her grammar in public, but it was predictable that he would think it was "wrong." After all, he is 39 years old, and she's 22.