Sharp, sensuous lines — the kind that define young rowdies in fine old photos — soften over time.

The long, lean muscles that keep hard-chargers two steps ahead of the yapping pack slacken, usually about the time the razor-cut, pinstriped wolves in back pick up the pace.

And suddenly, the smooth-faced kid with the green iPhone, the one who wears extremely skinny jeans and pointed shoes, gets all the choice assignments, not to mention your parking spot.

But don't take the word of an aging boomer whose retirement plans will probably involve an old Airstream trailer somewhere in Arkansas — a sort of hillbilly version of The Rockford Files, the Rockabilly Files, I suppose.

Just ask Hyundai.

Back in 2009, Hyundai's midsize Sonata sedan absolutely crackled with tight, taut new styling, giving a once-invisible car instant status in an extremely tough segment.

In one model year, the Sonata shot to the front of the pack design-wise, lording its hot lines over boring Camrys and Accords and Altimas.

Hyundai must have tired of the race, though — or maybe its top designer moved to Colorado to open a pot shop — because the restyled 2014 Sonata arrived looking suddenly soft and safe.

I initially thought: Get back to the gym. Quickly.

Not that there was anything unattractive about the quietly handsome car. It just resembled all the other ToyHonNisses in the midsize world.

Give me any one of them in white with a $219-a-month payment and I'll try not to lose it on the mall parking lot.

So I had high hopes for the 2015 Sonata Sport 2.0 T, a saltier version of the Sonata with stiffer suspension, better steering and a more powerful turbocharged four-cylinder engine.

In the last version of the Sport, the turbo 2-liter twisted out 274 eager horsepower.

Moreover, the Sonata Sport I had recently came coated in rich dark-orange paint, looking as if it were ready to run.

Like the 2014 model, this year's Sonata starts strongly enough with giant, elongated headlamps offset by a large horizontal three-bar grille.

A fairly long hood that gave the car a hint of power stretched back to a sleek, rakish windshield.

But it all kind of sagged from that point on.

While clean and well-proportioned, which is about all I aim for these days, the Sonata lacks its former edgy distinction.

A conservative character line above the door handle traveled straight and true back to wrap-around taillamps, while a second, slightly more dramatic line down low eased some of the slabbish feel in the car's sides.

Still, the Sonata had that turbo motor beneath the hood and pretty decent 18-inch wheels wearing reasonably assertive 235/45 tires.

It seemed to have promise.

As I discovered, though, the 2015 turbo motor got de-tuned, possibly in keeping with the new car's more subdued nature or maybe just to scratch out a few more miles per gallon.

This year's Sport cranks out 245 horsepower, a nearly 30 horsepower drop in a 3,600-pound sedan.

And it's noticeable, particularly if you have passengers or are pushing it.

Both Car and Driver and Motor Trend found that the new Sonata Sport needed 8 long seconds to accelerate to 60, which is not even remotely high-performance and 1.9 seconds slower than the previous-gen Sonata Sport.

But I wouldn't necessarily recommend that you skip the Sport and save the $8,000 difference between the entry-level Sonata and the Sport (mine had a window sticker of $29,510).

For one thing, the front-wheel-drive Sport gets a tighter suspension that keeps it flat in most corners and makes it feel considerably more responsive.

Ride quality doesn't suffer much, either. The Sport is appropriately firm but has decent wheel travel and doesn't beat occupants up much.

Although the steering lacks the refined feel of the unit in the larger, more expensive Hyundai Genesis, it is still quick and well-weighted.

And believe me, that is an enormous accomplishment for Hyundai, which once had some of the vaguest, strangest steering in the business.

In addition, the turbo 2-liter churns out 260 pound-feet of torque at a really low 1,350 rpm. As a result, I didn't realize at first that the Sport was so average in acceleration.

With all that torque down low, the big sedan charges away from stoplights with more than ample energy, running briskly through its six-speed automatic transmission.

It even gets decent fuel economy, squeezing out 23 miles per gallon in town and 32 on the highway, and sounds better, adding to the car's overall athletic feel.

If you want a livelier Sonata, the Sport is still worth considering.

No major compromises, though, were inflicted on the car's black interior.

Sure, like all midsize sedans, the Sport had plenty of hard plastic, from its softly curved dashboard to all the door panels.

But this generation of Sonata feels more German inside than the last car, which flashed a giant center stack in the middle of the dash that dropped all the way down to the console.

It always looked to me as if some large metallic object had blasted into the interior.

The new Sonata features a 6-inch touch screen with a more subtle horizontal panel beneath it for the climate controls.

The door panels, while plastic, offered padded centers with orange "stitching" on the panels.

Likewise, the nice-looking black leather seats had perforated centers and orange stitching on their bolsters.

In back, the seats provided good headroom and legroom in spite of the Sport's curving top.

Even with the substantial $8,000 premium for the Sport version, the Sonata is still a pretty good deal — at least $3,000 below average new-car transaction prices in the U.S. with all its options.

But I wish the Sonata would shuck its Jos. A. Bank suit and slip back into its tattered black leather jacket.

The Sport has most of the basic right stuff to be a mild-mannered rebel again.

And the staid midsize sedan segment needs all of those it can find.

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ABOUT THE WRITER

Terry Box writes for the Dallas Morning News. He may be reached at tbox@dallasnews.com.

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