Cable is beginning to discover what many of us already knew — namely, that getting older kinda sucks.

For years, cable channels enjoyed unfettered growth, with rising subscriber totals and increased fees from cable operators. In the last few years, the desire to be even bigger (and richer) has led to programming and even brand/image makeovers — which explains why there’s less history on the History Channel, less learning on TLC and only occasional arts at A&E. Instead, programmers have crammed into the reality TV pool, displacing plenty of water but failing to lift many boats.

Now, cable has reached its maturation point; suddenly there is heightened pressure to deliver ratings that translate to revenue, triggering a huge scrum for advertiser-friendly viewers.

And guess what? Forced to act like broadcasters by tussling for every last adult between 18 and 49, cable gurus appear as dazed and confused as their older-media brethren.

In short, cable is entering middle age, while the major networks — having already experienced the whole sports-car/comb-over midlife crisis — have generated an inordinate amount of noise.

This year’s “it” shows come not from MTV or Bravo, but from ABC, whose newest cultural phenom, “Desperate Housewives,” has stormed the Sunday-night parapets once seen as the exclusive fiefdom of HBO.

The tightening spigot begins with cable-system operators grappling with aggressive satellite services, especially now that DirecTV falls under the aegis of wily News Corp. The competitive mantra has become finding ways to bundle new services and thus boost income, though with phone companies greedily eyeing the same market, it’s not clear how that faceoff will pan out.

Operators also have consolidated and grown, making them less pliant about paying the annual fee increases that once kept cable-channel stockholders fat and happy. Although the notion of a la carte cable proved a nonstarter at the regulatory level, politicians are smart enough to recognize that no constituent appreciates a higher cable bill.

Facing all these concurrent threads, cable channels — determined to meet the demand for rising profits — must emphasize ratings, especially among the younger adults coveted by media buyers.

Even ESPN, with its enviable sports niche, has gone Hollywood, gambling on scripted series and movies (such as the poker-driven drama “Tilt”) in its effort to lure more than just beer-soaked guys back to headquarters in Bristol, Conn. HBO, meanwhile, finds itself struggling to remain buzzworthy when its rivals want the magazine covers and New York Times thinkpieces that seemingly became its birthright.

Cable still enjoys formidable advantages, the foremost being a dual revenue stream (subscriber coin plus ad dollars) that alleviates some of the pressure broadcasters face. Moreover, the conglomerates running the networks also own cable outlets, so talk of the broadcast-cable divide often obscures the fact that the two frequently act in concert, from NBC showcasing sister cabler Sci Fi’s “Battlestar Galactica” to Viacom’s CBS garnering its kids lineup from Nickelodeon.

The true lesson is that the alchemy of producing hits isn’t particularly well served by chasing the same narrow slice of the viewing pie. If anything, ABC’s swing-for-the-fences approach — highlighted by programs developed by a management regime ousted months earlier — suggests there is something quite liberating about lowered expectations.

That once was true for cable, since hit series were a relatively recent addition to the programming stew, drawing attention to networks like FX, Bravo or Comedy Central. When FX’s “The Shield” premiered, officials all the way up to News Corp. chief operating officer Peter Chernin had a “what the hell” attitude, as if there was nothing much to lose.

By contrast, those channels’ new offerings are now measured against past benchmarks, which might explain why the creative well has temporarily run dry. Because after reveling in the exuberance of youth, it’s not always as much fun to be a grown-up.

Extreme Makeover: News Edition: Speaking of the obsession with youth, amid the tumult over choosing Dan Rather’s replacement and revamping “The CBS Evening News” has been the question of whether young adults can be enticed to begin watching evening newscasts.

The answer is “sure,” assuming one or both of the following happens: The U.S. reinstates a draft that applies to everyone up to the age of 34; or space aliens abruptly saddle all teen, twenty- and thirtysomethings with a mortgage and 2.3 children.

Otherwise, party on, gang, and let the older folks watch news and worry about the state of the world on your behalf. Having glimpsed your future, here’s one vote for delaying that process until you absolutely have to join in.