Definitely not too casual for a bday dinner, unless you regularly dine at The French Laundry. Tapas menu with some other expanded plates. Get a table out back, above the creek and you are in. Take him next door to Frog and Peach for a beer or a nice whiskey to get him relaxed.
Even better selection: Ciopinot!!! This is "THE" place to go, right now. wonderful atmosphere, great seafood, excellent wine selection. If you bring your own bottle, there is no corkage, I believe, too. Reservations a must.
Another spot: Buona Tavola. Great italian food. always packed. Get reservations for a spot on the back patio if the weather is nice. Indoors is nice and cozy, with good energy, too.
Hope that helps. Amy was right about Sycamore Mineral Springs. Great place to pull in for an hour and relax in an outdoor tub on the side of the wooded hill. Very nice. Sulfur smell is pretty strong, so bring some sweats and the like to get into afterwards. Don't want your good clothes to stink.