You'll want to wait to be higher. Iron I think is like 125 to mine, and is first found in level 25+ zones (Duskwood, Hillsbrad, 1k Needles). Tin is tough, but you have to mine it until you make 125 skill; for this, there is a cave in the Wetlands that will suffice quite well, despite the level 21-23 spiders there. That's your best bet!