If you are talking about The Great Wolf Lodge in The Wisconsin Dells, it is an awesome water park for all ages. I believe they have life guards so I wouldn t worry about the adult thing. Yes it is expensive and you have to book it well in advance. I am a 54 year old big kid and I have a blast in water parks. They are fun for all ages. Go for it. If you cannot get in to the Great Wolf, there are a number of other water parks there as well.
I think your age group would have fun, it would be somewhat expensive, and you will need supervision depending on your parent s decision