Which type? Children have absence seizures with whole brain 3/sec spike and wave. Young adults have absence seizures from a focus in the brain. These may look the same when you see them, but they have very different causes and prognosis. Petit mal ("small bad") usually is used for the childhood form. A quality eeg interpreted by a good neurologist can make the distinction.
Variable. The term "petit mal" is an antiquated term. It was used in the past to describe seizures that were not convulsive in nature. In the past few decades, the categorization of seizures has changed dramatically. Petit mal seizures are typically one of two types of seizures - absence seizures or complex partial seizures. The prognosis varies widely between the two.