No, there aren't any adult-only hotel-casinos in Las Vegas. When Bellagio opened in 1998, the city was already abandoning the "family destination" marketing spin of the early '90s and Steve Wynn set a new precedent by initiating a no-children policy at his new property. This meant no one under 18 was permitted unless they were a registered guest of the hotel, had tickets to a show, or were in a party with reservations at one of the property's restaurants.
At the time, the PR spin on the no-kids rule was that it was to avert overcrowding on account of the overwhelmingly popular demand to look around the new hotel, although it's more likely to have been due to the desire to achieve a sophisticated adult ambience throughout. That policy is no longer enforced and kids and strollers are now welcome. Likewise, the other properties in what was previously Wynn's group – Golden Nugget, Mirage, and TI – no longer have the no-stroller policy that was in place under the former owner.
At one point, when they were all excited about filming the Ocean's trilogy here, Brad Pitt and George Clooney talked of opening a sophisticated resort-casino with a dress code but in June 2006 the Las Ramblas sales office was closed and the 25-acre plot of land the hotels, casinos, and play areas were to stand on sold to the developers of the neighboring W Hotel, Casino & Residences -- which also never happened.
Wynn and Encore permit children of non-guests to visit but enforce a no-stroller policy (although we have seen them on property). A call to Aria revealed that children are welcome. These three would probably be our recommendations as far as more sophisticated adult-oriented ambiences are concerned, however.
Of course, all casinos are bound by Gaming Control regulations dictating that no under-21s should stand around in gaming areas, and many shows and some restaurants are restricted to those 18 years or older. Many hotels don't permit anyone under 21 to check in (see QoD 3/29/2010).
