Mary Kate Olsen's romance with new boyfriend Olivier Sarkozy, the younger half-brother of former French president Nicolas Sarkozy, is reportedly getting more serious.

Although the couple has a 17-year age gap -­­- Sarkozy is 42, while Olsen is only 25 -- they are apparently so serious about each other that Sarkozy recently purchased a $6.25 million townhouse in New York's East Village, the better for the two to spend more time together.

According to a source for the New York Post, Sarkozy decided to purchase the 146-year-old townhouse because he and Olsen "like that it is old." The historic 4,200 square-foot home comes with five bedrooms, four baths, eight fireplaces, and a "Juliet balcony" on the second floor. The townhouse was designed by James Renwick Jr., who is better known as the architect of St. Patrick's Cathedral, the Smithsonian and the Main Building at Vassar College.

The couple have been spotted together multiple times in public, celebrating Memorial Day weekend in the Hamptons, cozying up at a Knicks game, and even going out for a stroll with Sarkozy's 11-year-old daughter.

"M.K. is constantly complaining about boys not being mature enough for her," a source told US Weekly. "She got the kids out of her system. Now being a businesswoman dominates her time, and she is rarely impressed with guys."

Olsen and Sarkozy, who is currently co-head and managing director of the Carlyle Group, a powerful and well-connected private equity firm, have been dating for only about five months, but their relationship has already come under fire from Sarkozy's ex-wife. According to the National Enquirer, Charlotte Sarkozy, who has two children with Sarkozy but separated from him in 2010, said of the budding relationship, "That's not right. It's grotesque." And a source added that Charlotte's disapproval didn't end there, saying, "Charlotte certainly won't want her kids to be around Mary-Kate, who has a history of wild partying and booze binges."

In the past, Olsen has been romantically linked to a number of eclectic partners, including David Katzenberg, the son of Dreamworks CEO Jeffrey Katzenberg, hockey player Sean Avery, and Greek shipping heir Stavros Niarchos III. Olsen hinted to W Magazine in 2005 that her breakup with Niarchos, which happened soon after he began dating Paris Hilton on the side, was the primary reason that she dropped out of NYU.

Prior to getting together with Sarkozy, Olsen dated artist Nate Lowman for two years, before splitting in 2010.