It's a mashed bullet, in that condition that's all you can really find out. It could be 30 years old, or 130 years old. Typical oxidation from being in the soil.
The oxidation product of lead is white lead oxide, forms over time in the soil on metallic lead. Remember lead based paint??? It was white because of this lead oxide product. Not really poisonous unless ingested, so after handling it, just wash yer hands!