That should be plenty of yarn, you might even be able to get a hat and cowl out of it, depending how big he wants it. PRobably wants something like a neckwarmer which would be about 22-24" around, just enough to go over his head but fit snug around his neck. So cast on about 20 sts and work a couple inches, see how many sts per inch you get, then multiply that times 23 and cast on that many sts. For a stitch pattern you can do about 4 rounds in garter, then stockinette and finish with 4 rounds of garter, or use another pattern. You can probably find a lot of plainer cowl patterns (no lace or long ones) at
www.knittingpatterncentral.com or
www.dailyknitter.com. Knitty.com has some that could be used for a man, so does lion.com