I'm sure this all depends on the type of personalities involved as well as the type of vacation you are looking for. But for instance, I'm 25 and my husband is 27 when we traveled to Aulani for our honeymoon and we had a spectacular time. I don't think we could have picked a better place for us if we tried!
There is plenty to do for adults, adult only pools and infinity edge hot tubs where you can watch the sunset. The beaches are perfect and plenty big enough to be able to shy away from the families (if thats what you are looking for). You can snorkel and paddle board. The spa is HEAVEN. The restaurants are delicious. The resort as a whole is gorgeous! If you are looking for options that has less families or kids then Ama Ama is your best bet. My DH and I are huge Disney fans, and we love kids, so having families with kids around us doesn't bother us one bit. I think there was actually less young children there then I was expecting there to be. Of course, there definitely was children, but never once were we bothered. Not by the pool, or at dinner, or in the lobby or anything.
We loved the adult pool. Although it doesn't have much to it, its in a nice quiet corner of the pool area, and it's never really too crowded. There's a pool side bar as well.
We aren't beach people and we literally went to the beach like 4 times during our 8 day stay. We were really only expecting to go once. But the beach was so beautiful and relaxing that we used it much more then we thought we would. The pools and hot tubs were more so our favorites.
Aulani was a perfect place for a couple. My DH and I would go back in a heartbeat, and we are dying to. There are plenty of things to do for fun, adventure and excitement, as well as romance and relaxation at Aulani for you guys! And just across the road is a group of other restaurants that you can visit. Monkeypod has great food for lunch or dinner. As well as something for night life. Live music, apps, drinks, etc!