Here is a script that does what you want:
Names Default to Here( 1 );
test_here = Graph Builder(
Variables( X( :Column 6 ), Y( :height ), Color( :sex ) ),
Elements( Points( X, Y, Legend( 3 ) ) ),
SendToReport(
Dispatch(
{},
"400",
LegendBox,
{Legend Position( {3, [0, -1]} ), Position( {0, -1} )}
)
)
);
upper_bound=70;
report(test_here)[axisbox(2)] << Add Ref Line( upper_bound, "solid", black, "", 2 );
Jim