Young people are indifferent to Twitter, a hot topic the New York Times is mulling today. But no one's really figured out why. Our theory: Young people have lives, and Twitter is for creaking shut-ins.

Don't get us wrong. Not everyone on the microblogging service wants for real-life social interaction. Celebrities like Ashton Kutcher and Oprah Winfrey get invited to plenty of hot parties, and use Twitter more for self promotion than anything else.

But the rest of us? We're old people — a.k.a. adults — who don't actually see each other as often as we'd like. We've got significant others, kids, and — if the economy has been kind to us — time-consuming, energy-sapping jobs. And old mature farts don't have a huge cache of beer-chugging party photos to upload to Facebook, or hours to spend indulging in-depth symmetrical relationships on that social network.

Hence, Twitter. It's not a supplement to a social life; it is a replacement social life. It's no accident that the site was started by thirtysomething programmers and technical book authors, and that some of it's earlies adopters were freelance writers, some of the loneliest people on the planet. Which isn't to say this core constituency makes Twitter any less interesting, or worthwhile. If anything, it's the reverse; what was the last pop culture trend created by shut-in adults?

(Pic: Twitter co-founder Jack Dorsey, a programmer whose social life appears quite active in the wake of his creation. By Joi Ito.)