Sorry I should have looked around before I posted but I found one of the physical reasons for higher 17 OHP in preemies and newborns below:

"Adrenal function undergoes significant changes during the neonatal period. The adrenal glands of a new-born are the same physical size as those of an adult due to the presence of an additional ’Fetal’ zone between the medulla and cortex. This zone produces large amounts of androgens and is the major site of steroid production at term (>200 mg DHEA per day, adult production 20 - 30 mg/day. Cortisol 25 mg/day.) and is progressively lost during the first 3 weeks of life. This change is accompanied by a decrease in androgens (and therefore 17OHP and other intermediates) with constant cortisol levels. Premature infants or neonates with delayed development may retain this zone for longer."

and you can find that here:

http://members.aol.com/Richstott/17ohp.htm

I think it is like I said that the preemies adrenals are a little behind a newborns adrenals and perhaps it just takes longer for that zone to diminish, which means higher than normal levels for a longer period.