I didn't get any rare items until level 18 (have 5 or 6 now) and just got my first legendary engram drop at lvl 20 but that got decrypted into a rare. Of course this can vary quite a bit from player to player. Best tip I can give, which you probably already have read, is concentrate on the bounties to level up quick and upgrade your gear. Always check your equipped gear before turning in a bounty and make sure you have as many upgradeable items equipped because all that xp will go to the gear to. Even if you don't plan on using something right away you can switch it back. I think I'll be grinding toward buying my gear and hopefully get a little lucky along the way. Have fun!