Hello kjp and welcome to cruise-chat--I see it's your first post, although you've been registered a while. What a wonderful thing to do--surprise your parents with a cruise!
A six day cruise on Golden Priancess would be the ideal introduction to cruising. Princess offers the kind of cruise experience that can be enjoyed equally by someone in their 30's, 60's and 70's.
My wife was on Golden Princess in October, and she said the ship was in beautiful shape; and the food and service were the high quality we have come to expect from Princess. Plus, the six day will give you a nice mix of relaxing sea days and interesting port days.
So have a wonderful trip, and keep in touch.