Unfortunately I don't think there's not much you can do to stop those kinds of threads barring flat out locking them or stopping new people from posting, which would not be the best for a forum if you want to encourage people to join (even if the repetitive advice threads from first time posters get annoying).
Newcomers typically don't read stickies/ignore stickies and the majority of people finding this forum are young kids doing searches for board related help, so those board advice threads are just a result of the demographic of traffic that finds it's way to the snowboard forum.
In the past I've tried going as far as making detailed 15 min videos breaking down how to size and pick a snowboard and kids still comment on my sizing video asking me what size board they should buy because they're too lazy to even watch the video and follow the advice in it.
Unfortunately if they won't even watch a video, you can bet they're not going to read through long forum threads to find the information they need. It's just something we may have to live with in exchange for having a popular snowboard forum that shows up high on a lot of snowboard advice searches.