Hi, I can recommend the Zante maris hotel in Tsilivi Zante It is right on a beautiful sandy beach and a stones throw away from the bars shops and tavernas. We are a couple in our mid 40's and there was a good mix of ages when we were there. The hotel is lovely and the food was excellent with nightly entertainment if you don't feel like venturing out. We booked through Eclipse direct as it was slightly cheaper then first choice.

Another place we enjoyed was Tingaki in Kos where we stayed at the mythos appartments which where brilliant 100mtrs. from the sandy beach and right in the centre of the resort but very quiet. You could also book Half board here but we liked to eat at differnt places though the restaurant at the mythos was the best one we tried and very reasonable. A group of us stayed here to celebrate a fiftith birthday and had a great time.
These were booked through Thomas cook.
I hope this might help.