Is it ok to fill a pandas dataframe with NaN values? Is it correct to fill a pandas dataframe with NaN values? In specific: if I have a dataframe with a user name and his age is it ok to fill the age column with int and NaN values.
Names  Age 
Lisa   25
Jack   NaN
Tom    32

Later on I want to work with this dataframe, will I get any problems if I have NaN values in it?
It depends on what problems you are afraid of:

regarding &quot;technical&quot; issues, it should be ok having NaNs in your dataframe and, afterwards, applying the pd.isna(column_name) per attribute to get a boolean mask to find those unknown values per column, more info here
in case your problem is not knowing the actual values, one option is imputation, but not all types of variables are easily imputable (neither it makes sense to impute all of them)