What about a child over 18 in college. Can he have his own apple ID without a CC and still do family share?

Yes. Family Share can be used with adults as well. There is no age limitation for Family Sharing.

However, there is an age limitation for the "Ask To Buy" feature. Ask To Buy cannot be enabled on accounts older than 18 years of age.

More details can be found in this support documents:

Create or use your Apple ID without a payment method - Apple Support

Family Sharing - Apple Support

Request and make purchases with Ask to Buy - Apple Support

Also note that his college must be in the same country as you, since the Family Sharing group is tied to the country's store of the Organizer, and cannot be used by anyone outside the country.