We claim the ornamental design for a youth staircase, as shown and described.
FIG. 1 is a top view of the youth staircase;
FIG. 2 is a front view of the youth staircase shown in FIG. 1,
FIG. 3 is a rear view of the youth staircase shown in FIG. 1;
FIG. 4 is a right side view of the youth staircase shown in FIG. 1;
FIG. 5 is a right side perspective of the youth staircase shown in FIG. 1; and,
FIG. 6 is a rear right perspective view of the youth staircase shown in FIG. 1.
The bottom of the youth staircase, not shown in the drawings, is flat and devoid of surface ornamentation. In addition, the left side of the youth staircase, also not shown in the drawings, is devoid of surface ornamentation.
The subject matter shown in dashed lines, and any surfaces of the design not shown, including interior surfaces, form no part of the claimed invention.