For myself, whose favorite sports are the tri (surf skate snow), I learned all 3 as a teenager (sk8 a little earlier), snowboarding had the shortest and steepest learning curve. Learning to surf takes learning to paddle, which can take a really long time, not to mention just building the muscles required to paddle for 4 hours. Riding a skateboard basically is pretty easy, but the motor skills required for techinical skateboarding are unmatched in the other 2 sports. On the other hand, the outdoor prowess of watermen like Laird Hamilton and mountainmen like Jeremy Jones - nothing like this is found in skateboarding.
Being comfortable in the stance is definitely going to put you a step ahead. Snowboarding is truly easy to learn, but it's also very foreign at first, and it won't seem like its as easy as you thought it was going to be. Be prepared to fall HARD, as catching edges tend to whip you face and ass first like a wet towel.
At your age, take a lesson or 2 and it will be ALOT less painful (I'm also turning 37 during the season. Year of the Dragon wup wup!).
is it late october yet?