So far so good - you made great choices in flying in a day early and you picked a nice hotel with a shuttle to the ships.
Ruby is a beautiful ship - very palatial yet comfortable. You will find the average age is slightly older on Princess than some other cruise lines, but the ship carries over 3000 people, so I am sure you will make some friends of all age groups. Besides that, "older people" can be just as cool as other people - unless you need to talk about your favorite bands or something else where age really matters.
But really, it is more a matter of where you go on the ship. If you go to the dance clubs and hang by the pool you will find plenty of younger people.
More importantly, just concentrate on what you plan to do on the ship and on shore as a couple - whether or not you meet people on board, you will still be able to create a lot of memories for each other.