It turns out that age matters a hell of a lot, independent even of experience. Teenagers are horrific insurance risks.

A provisional license offers both supervised training and effectively delays entry into the unsupervised insurance pool by a year.

After this, location (e.g., ZIP Code, in the US) and miles driven are the biggest predictors. Latter are why insurance companies will do almost anything to get ahold of odometer readings.

Source: Worked on auto insurance risk products.