Romance, Satire/Parody, Tragedy
Romance
The Age of Innocence is a love story, and a love story of the best kind: two star-crossed lovers who clearly belong together but are kept apart by mean people. It's the same formula you see in all the great love stories — Romeo and Juliet, Wuthering Heights— and practically every soap opera. There's just something so dang romantic about impossible love. Yearning is cranked up to eleven, no one is getting sick of each other's weird habits or nose hair, and there is so much sighing.
But this novelis also a romance of a different kind —a romance with a period in history. You know the cliché of good girls falling for bad boys, a la Grease? This is essentially the kind of romance between Edith Wharton and New York of the 1870s. Edith Wharton knows that New York in the 1870s is no good and will break her heart, but she can't stop talking about how good it looks. New York in the 1870s is a heartbreaker, but an irresponsibly handsome heartbreaker.
Satire/ Parody
What do you get when you depict a powerful and ludicrous force with the intention of showing everyone just how freaking ludicrous it is? Yep. You get satire. And what better powerful force to make fun of than the stifling environment of New York high society in the 1870s?
Although Wharton mesmerizingly depicts the nifty décor and the awesome fashions with a detail that almost warrants the adjective 'loving,' we're not supposed to root for, say, the Wellands. Why? Well, flip to any page in the novel and you'll find an instance of members of New York high society acting like real d-bags, and then hiding behind a veil of proper morality. That's worth poking fun at on any day of the week.
Tragedy
Our handy-dandy tragedy definition states that a tragedy sees a noble character fall from grace. Yup. The Age of Innocence nails this, and it nails it in two ways rather than just sticking to one.
OK: Newland is our noble guy. He's really a stand-up dude, even if he's a dilettante and a little pretentious. He's good to his family, interested in the world, and does some good stuff.
But does he ever fall from grace. This is where the "double tragedy" thing comes in. Within his own society, he falls from grace when he falls in love with Countess Olenska. Within the world of the novel (a world that believes in love and freedom), he falls from grace when he doesn't have the cojones to follow through with his love. Newland is tragic no matter how you look at him.