Rick,
HBARPARM also can do that .

data NationalAverage; /* fake data for demonstration purposes */
label Average = "National Average";
input Age Average Low High mean;
datalines;
11 60 53 63 60
12 62 54 65 62
13 65 55 67 64
14 66 56 68 63
15 67 57 70 65
16 68 58 72 66
;

data All;
set Sashelp.Class NationalAverage;
run;

proc sgplot data=All noautolegend;
hbarparm category=Age response=mean / name="S" legendlabel="Class";
series y=Age x=Average / markers datalabel=Average name="Avg" legendlabel="National Average";
highlow y=Age low=Low high=High;
keylegend "S" "Avg";
run;