Most of the resorts on the island are small, and even if there are kids it's definitely not like being at a hotel at DisneyWorld.
Condotels tend to attract families with kids due to the extra room. Your best bet for a place without kids probably would be an expensive spot like Mata Chica, or a hotel with rooms only, not suites, such as Tropica, Changes in Latitudes, The Tides, etc.
--Lan Sluder