G'Day,
I'm a cranker. About 450rpm according to Alan Chen of Brunswick. "Old School" as Samael puts it, although working on my release to accommodate new technology.
Bowl however you want, as long as it brings you joy. Being a cranker makes it tougher some days and easier others. Getting a coach to supervise you is excellent advice. Ed Kee, Stuart Erwin, Eric Jang and others (I grew up in Sydney) taught me so many things that not only made me a better player, but probably saved my back, arm and other joints a lot of pain. Cranking the ball is hard yakka! It's only after months or years of slog that it gets easy, because you've built the muscle mass to accommodate this unnatural act. (Like pace bowling in cricket.)
If you want to be a cranker, then do it. But seek good help. Show your coach a video of someone you'd like to bowl like, so they know where you're headed and you can both work toward that goal. Carefully analyse what that person does with their forearm & wrist, then see where their feet and balance arm are while this is happening. It's like ballet. Everything affects everything else and it's a beautiful thing when it all comes together.
Don't settle for less, but know when to back off for your game and your health. All the good performances I've had came from using about 80% of my capacity. Don't twist it up for the sake of it.
BUT if you are going to crank the ball, watch for when you are in growth spurts. (You mentioned you're in school. So was I when I got serious about bowling.) During these periods, you can hurt your back trying to do too much if not properly supervised. (The joys of having a doctor as a coach!) At this age also, your timing gets screwed up as you get taller and your arms & legs get longer, so expect to have to tune things up from time to time.
You will also need a good ball driller. One who understands how to fit and lay out equipment for high revs. You don't need bleeding hands and blisters and all the crap I went through as a young fella.
Good luck to you! Be what you can be, but most af all
enjoy it!
Cheers,
Jason