Hello pm and welcome to cruise-chat;
first, congratulations on your son's graduation--what a wonderful way to celebrate. Be forewarned--cruising can become addictive--ask anyone on this site.
Since you posted on the Holland America forum I assume that is the line you are interested in--and an excellent choice it is!
The best advice I can give you is, seeing this is your first cruise, get together with a reputable travel agent that specializes in cruses; once the agent knows a little about you, he/she can make appropriate recommendations; how long a trip you want to take, what your budget is, do you want to include a land excursion; these all need to be considered.
Being your first cruise, I would suggest starting easy--a 7 day Inside Passage round trip from either Vancouver or Seattle.
Of course you may have something much more elaborate in mind. This is why you need to sit down with a cruise professional--and I would do it pretty soon. Assuming you are talking about May of this year, I wouldn't wait to long, as your choices could become limited; Alaska is a popular destination.
Whatever you decide, have a wonderful trip and congratulations again.