I ended up ripping back my first attempt with making the Elk Watch Cap. I somehow or other managed to have an extra stitch picked up at the end of the round. I followed the stitch down and found a yarn-over that I had picked up and purled on the 10th round. Well, crap! I pulled out the needle and before ripping it, I test fit on my own head. Nice fit. My head is 23-1/4" (59 cm) and my son's is larger than mine. I do believe a few more stitches will fit him better.
In addition to the above mistake, I wasn't happy with how holey the fabric appeared when stretched so I chose to cast on using a smaller circular needle and increased the cast-on total to 208 stitches (a quick swatch on size 1 (2.50 mm) circulars gave me 8.5 sts to the inch.) My actual cast-on is on a size 1 (2.25 mm). I have about 1-3/4" (4.5 cm) so far. I keep being distracted by reading blogs.
Oh, and for those who question long tail cast-ons, I measured 104" and threw in an additional 4" of yarn for good measure. Here's how much was left after I finished the (2 needles together) cast-on.