The single most "romantic" restaurant in Houston is Aldos Con Amore. But I think it shut down. Marks is awesome. Rainbow Lodge and Brenners are super nice. Fogo might be my favorite restaurant, but its not really romantic.
If you're 12 years old. Riley, if you're looking for French go with the aforementioned La Tour d'Argent or La Colombe d'Or.
Mark's was the first thing that popped into my head, but one of the most romantic places I've been to around here was actual Chez Nous in Humble. Yes....it is out in the burbs, but it could fly anywhere. Excellent French cuisine in a nice atmosphere (in an old house). http://www.b4-u-eat.com/houston/restaurants/reviews/rsv0128.asp
Aldo's on Westheimer shiut down?????? NO WAY!!!!! That place was amazing. Fogo is anti-romantic. You could have kids running around. Marks is amazing if Aldo's is no more.
Marks is nice...food is avg but good for Houston. Strip House or Pappas Steak House is nice too...as is the Palm.
Best Pork Chop in the city! I've never had a bad meal at Marks. Fogo is great if you want to eat a lot of meat. Not really romantic though.
More party atmosphere, but I like La Griglia on West Gray if you are in the mood for fish. The crab/ shrimp cheesecake appetizer is awesome. Good wine selection if you like wine. Vic and Anthony's near Minute Maid park-excellent steak and very good crab cake. I know these are both Landry's restaurants, but La Griglia wa a Tony Vallone eatery until recently. It is still good. For romance I like Back Street on Shepherd. Excellent wine list.
Or Olive Garden. (y'all seriously need to stop taking your women to these restaurants if you plan on keeping them, unless you have a lot of money you like to piss away. They'll get accustomed to it, which will leave to the inevitable heartbreak when she dumps you because you're broke.)
Mark's is within a renovated church turned to restaurant off westheimer. It's very loud though in the dining room because of the wooden floors etc. Upstairs, it's more romantic because of the candles. Ruggles-Grill 5115 within Saks in the Galleria is pretty decent. It has a nice dim lit setting.