If you both go into this with a sense of fun, I think you two will have a great time. The castle itself is a nice place to spend time, the staff is nice, and most teen boys I know would be more than happy to stuff themselves at an all you care to eat breakfast. The princesses will probably refer to him as a prince, and I bet any photos you take with them would bring up great memories later on. Have a great trip!
Edited to add: As for the food, we've eaten breakfast here twice and enjoyed the food both times. The potato casserole is a big hit with all three of us. The scrambled eggs remind me of my grandmother's, so I LOVE them and I don't usually have an opinion about scrambled eggs. The cold bar is our favorite. My husband fills up on smoked salmon. I love the peppered mackerel, and our daughter and I both love the gtetost cheese which we pair with the croissants. The strawberries have been deliciously fresh both times we've been there, too.
Trust me i've seen grown men dine solo at character meals. Nobody cares. You'll be totally fine. Have fun!
it was the best. 
