Age does funny things to people. It morphs scrawny, punked-out teenagers into respectable members of society and sometimes the transformation works in reverse — as in the case of a midlife crisis. The same goes for a lot of musicians and bands out there. There’s a developmental cycle to many a music group and the same complaints from fans stretch across generations. Arctic Monkeys have been a band for eleven years now and are on their fifth album with “AM.” So it should come as no surprise to anyone familiar with the musician-fan developmental cycle to be ready for cries of “they’re just not as fun as they used to be.”

And, you know, it’s true. Their debut record, “Whatever People Say I Am, That’s What I’m Not,” has gone quadruple platinum and sold 360,000 copies in its first week when it dropped in 2006. They’d generated press before that with online demos and interest grabbers. The USA had The Strokes while the Brits had the Arctic Monkeys. Frontman Alex Turner was only 20 when the album debuted and his songs showed it. “I Bet You Look Good on the Dancefloor” as well as “Teddy Picker” and “Fluorescent Adolescent” from “Favourite Worse Nightmare” are all really youthful, fun and danceable songs. And “AM” doesn’t have much in the way of that.

The mistake is going to be saying this is an inherently bad thing. But it’s just important to remember stages of development here. When Turner was 20, he was making the best music any 20 year old could make — music about bouncing around, freedom and frustration, all those collegiate qualities known far and wide. But he’s 27 now and he knows it. There’s something to aging gracefully and being closer now to 30 than 20 that brings certain elements to bear on life as well as music — more restraint, maturity and slow-paced introspection.

That’s not to say there isn’t plenty of time for good rock ‘n roll here. Opening song “Do I Wanna Know?” oozes grit and swagger, drenching itself in what made rock such a potent lightning bolt when it first arrived on the scene. It’s about a girl who hasn’t been that nice, a theme the muses seem to bless guitar-wielding artists across the globe with. And Turner tackles it in detached, sunglasses-on-in-a-darkened-room style that should rope you in if you’ve got any angst in your guts.

“R U Mine?” is probably the most classic sounding Arctic Monkeys song on “AM” and it’s also the best track on the album. “One for the Road” sets the tone for most of the songs to come after it. The majority of the other tracks here are more mellowed-out than the first two barnstormers. The grit is traded in for polish. It’s not quite a leap from punk to new wave. They don’t give up being Joy Division to become New Order. But there’s no doubt a sleeker sound than ever for the rest of the album.

Case in point: “No. 1 Party Anthem.” It’s a glam rock ballad akin to early Bowie and T. Rex’s most soft-spoken moments. Most apparent here is Turner trading in his old smart young punk’s snarl for a more mature near-croon. Though it’s different, it’s worth getting used to. The same goes for the rest of the record.

So, what are we to make of a band at this stage of development? Their youthfulness is what made them popular, of this there is no doubt. And it’s true they aren’t as fun as they used to be. But even though it may not be as good as the old stuff, it’s still pretty good. And, come on, it’s still kind of fun too!