How can I consider a flag var- "ASTATFLG" in my analysis?

I am requesting to get an idea on the use of flag variable in restricting my sample to those adults who had records during NHIS 2011-2015. Usually, analysts do

drop age if age<18.

However, I am worried about not to miss those respondents who are below 18 years and still consider as adults in some states. Therefore, I would like to consider “ASTATFLG” var to select my adult sample size. Would you please have any suggestions?

The ASTATFLG variable identifies if a record is a sample adult record. As detailed on the variable description tab, a sample adult is the one adult per family who was randomly selected to answer additional health-related questions. Therefore, if you want to limit your sample to sample adults who have records, you can keep all observations with ASTATFLG==1 “sample adult, has record”.