I've travelled solo often (still do). Depending on which H.A ship you're on, the older ones in particular, there will be a high senior passenger count so lots of people your age group. If you haven't cruised yet maybe have a travel agent book your cruise for you as they will know things you'll need for embarkation etc. & they may be able to save you some $$ if they have "group rates" on hold for the ship you want to sail on or they may be able to offer an on board credit to you for booking with them.
Sign up for excursions at various stops as you will be with others from the same ship and you'll end up seeing them around the ship later and find some will be eager to talk to you again about the shared experience. If dining in the dining room, choose seating with others. It may feel uncomfortable initially but as soon as conversation starts up, you'll feel at ease. You'll meet some people you like and some not so much but it's all good. There are also lots of activities on the ship you can attend such as trivia hours, excersize classes, movies somewhere onboard as well as other instructional classes such as learn to play pickle ball. Great places to meet others interested in similar things of interest to you.
Enjoy a couple of the specialty dining venues Hollan American ships offer as well. They cost additional but the food is top notch. Pinnicle Grill steak house is excellent for steak/seafood and the Canalleto Italian restaurant is fabulous for pasta and other special dishes.
Above all, remember, you're all on holiday travelling to an exciting new place so most everyone is friendly & upbeat. Saying hello to people around you on the ship costs nothing and many will not only return the hello but other comments as well.
I say, go for it! You'll be pleasantly surprised how much fun you'll have if you go into it with a positive attitude.