Congrats on your upcoming HS Graduation. Flowrider is alot of fun. A parent does have to sign the waiver. There will be days where the lines get long for the flowrider.
Can't give you advise on Not wrecking yourself. I wreked myself two cruises ago now I just watch (which is still fun). You should be fine on flowrider the kids/teens/young adults usually are it's when you get older that you have to be careful and take it easy.
My son is graduating on 6/24 he is spending a few weeks overseas in the summer to play soccer.
Freedom is a wonderful ship you will have a blast!!