I live in Anne Arundle County Maryland and am replacing my old dishwasher which is 18 years old. Do I need to still use an "air gap" between the dishwasher and disposal?

Do I need to still use an "air gap" between the dishwasher and disposal?
Yes you do! Either a counter top air gap or a high loop air gap, (see image) Over the years we have had no complaints on a high loop. We can't say the same thing for counter top air gaps.
Good luck, Tom