\begin{Schunk}
\begin{Sinput}
 range(dat$age)
\end{Sinput}
\begin{Soutput}
[1] NA NA
\end{Soutput}
\begin{Sinput}
 max(dat$age)
\end{Sinput}
\begin{Soutput}
[1] NA
\end{Soutput}
\end{Schunk}
