Either you are an extremely late bloomer, or your stuck with a small flaccid penis. In most cases flaccid penises erect longer then a big flaccid penis.

When a penis is not erect; it is Flaccid.

Flaccid means to be flabby and soft.
Don't exercise.

Yielding to pressure for want of firmness and stiffness; soft and weak; limber; lax; drooping; flabby; as, a flaccid muscle; flaccid flesh.

The term flaccid means something that is soft and limp. One might talking about a soft material that is not stiff and droops down in a flaccid manner.