Never use protagonists over the age of 25, or who have physical flaws.

Hm, the one I read violated this. The female lead was 31 and the book noted (though infrequently) that she was not physically attractive. And it seems that makes sense for a romance novel, since you're trying to pander to the fantasies of women who want to believe that they can have an exciting romance with a desirable man despite not being physically appealing or despite being past the ideal age.

The formula is basically to teach women as many dysfunctional, self-destructive ideas about romance as possible. Start with a young, never-married, beautiful, rebellious woman. Find her a dangerous, out-of-control, rakish, tall, dark, brooding, handsome man with many faults but a heart of gold, who has extensive sexual experience and has broken many womens' hearts. They have sex. He changes, tamed by her love and by her thighs; but remains dangerous enough to protect her in the future.

Yep. See: Twilight series.