Hey SAZ, I want you to read this it's about "surfer's ear"
www.lajollasurf.org/surf_ear.html
as you are 14, you may have not heard about this, and also as you say don't want to have anything covering your ears. I've only been kayaking 2 years and already if I don't have earplugs when I'm playboating I get instant ear aches that last all night. Anyway, as your young, you might want to start thinking about saving your ears. and if your in water that is cold enough to need to wear a skull cap, I would recommend you get one that covers your ears. Plus one that covers the ears keeps your head 75% warmer than one that doesn't (at least in my case). So I strongly suggest you get used to a lack of hearing, I did, and I go with earplugs, and a cap that covers my ears, and I come home ear ache free and worry free that my ear canal won't develop any bone growths.
Oh and the sweet strutters do have manufacturing differences, since they are hand made, some that say they are one size may be off by 1-2cms, I can speak experience to this becuz me and my buddy have the same size helmet, but his fits me more tight, and it's not the pads. I might get the one that's bigger on you, with the pads and straps finely adjusted you could get that thing fitting nice and snug, It took me awhile, but I got mine to fit very snug, and at first it was really loose. Good Luck. and please I hope you take the article into consideration.
BTW: surfer's get "surfer's ear" in water's that range from 50 degrees and up. when you consider most rivers are glacier or snow melt fed and on average, colder than 50 degrees. keep that in mind.
here's another article:
www.surfplugs.co.uk/About%20Surfers%20Ear.html
just imagine it says kayaker instead of surfer
Oh and in women, they reach skeletal maturation (stop their bone growth) around age 18, so your noggin may grow some more, but I expect your face will thin out and your head will grow taller, not wider.