That will depend alot on the parents.
how big are/were they?
one litter can have different sizes, such as runts obviously.
That being said, 18 lbs @ 11 weeks does sound a bit on the small side to me.
Neo's aren't quite as large as the English at maturity, but it seems in my experience that 18lbs should be more like 8 weeks...
I would love to see some pics!