Rick,
Maybe this is ugly. x2axis can be used in this scenario .

proc sgplot data=menstrual noautolegend;
scatter x=Users y=mean / yerrorlower=low yerrorupper=high errorbarattrs=GraphData1;
scatter x=Cycles y=mean/x2axis;
xaxistable age / x=Users location=inside; /* can use POSITION=TOP */
x2axis type=discrete ;
xaxis grid min=18 offsetmin=0.1 offsetmax=0.1 type=discrete;
yaxis grid;
run;