Why is Ant-Man Scott Lang instead of Hank Pym?

Why is Ant-Man Scott Lang instead of Hank Pym?

Hank is old now, which implies he was the first Ant Man in the 60s or 70s. Why though? Wouldn’t it make more sense for Hank Pym to be the Ant Man, as he is in the similar age group as the rest of the Avengers in the comics and tv shows. May 15, 2015

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