I'm 15 and trying to get into mountain biking with a 29er. I've decided on a Redline d440 and need to know if I should get a 19 or 21 inch. At the LBS I want to buy from, they don't have any in stock and require a deposit for a bike to be shipped out there, so id like to get this right the first time. I'm 6'1''(long legs too) with about a 33 inseam. I plan on doing some pretty flat trails but also want to introduce myself to mountainbiking too. Any insight would be appreciated.