I was thinking about how long an ink bottle lasts, and calendar time seems like a pretty poor comparison. A broad nib used for drawing can go through ink during a few long sessions, while a fine nib used for everyday notes may stretch the same amount across months. The way you use a pen probably matters more than how often you pick it up.
Counting fills from a bottle is a fairer comparison than months, though cleaning and ink left in the pen can skew it too.