What trace length is considered short in case of buck voltage regulator
As to loop area, while your design is probably fine as is -- there is one improvement you can make to it.  Simply rotate the output capacitor 180 degrees and delete any stitching vias that are in the way of the new routing for the Vout trace.  This shrinks both the D-Cout and the Cin-Cout loops, and makes it so they don't have to traverse stitching vias, either.

HOWEVER, you do have a problem with this layout that should be corrected before you go and get a board made -- the via connecting Cin to the Vin trace on the bottom needs to be not in that pad, lest it turns into a manufacturing headache, sucking all the solder away from that pad and leaving Cin disconnected on one end. Oops!