My first boat was a 12' Escape (rotomolded monohull). I got it when I was 12 years old. It was fun and easy to sail, and I sailed it all over the bay. But it wasn't very long until I was wishing for something larger. It could only carry one other person (and that was a challange at best), and by the time I was 16, I didn't really even fit on it anymore.
Additionally, the plastic cracked on the deck, and was a nightmare to fix. If any of you have experience with plastic welding, then you know that it really doesn't work all that well. The crack was in a location that was stressed, and kept breaking on me.
If I were you, I would get something made of fiberglass (NO PLASTIC). I would opt for a bigger boat - at least 17-18 feet. Also unless you are into racing, I really don't like small catamarans. They can't carry that much, have no storage, are wet, and uncomfortable. I think they are fun to sail for an hour or 2, and then my back hurts. I wouldn't really want to go cruising all day in one.