Wow, that's not incredibly cynical or kinda sexist on the part of those advice columnists or anything.
Contrary to popular belief (and apparently other advice columns), if a guy wants to commit when he's 18, he'll commit, regardless of how many women he's got lined up. Commitment isn't the last (or first) resort for everyone. Most guys want to commit at some point, but like a lot of women, they're not sure what they want in their lives, which muddies up the waters considerably.
If a guy wants to commit, he'll commit, whether he has no options or dozens. That simple. In fact, I'd recommend avoiding the guy running out of options, because in that particular scenario, neither person is happy; him because he committed out of desperation, you because you'll always be wondering when he thinks something better has come along.
Also, I'd stop reading the advice column at Douchebag Monthly: not a good source.
The guy I was with at 19 was also 19. He THOUGHT he wanted to commit, but he didn't really. After a couple of years he became very bored of us, with all of his friends going out and partying and hooking up with random people. So he slept with a bunch of my friends behind my back.
See, I'd been with someone else for a few years before that, and knew that what I wanted was stability and love. But while I'd had a couple of relationships beforehand, I was this guy's first relationship, and he didn't realise that he wanted to fool around a lot before settling down. Having been a virgin as well, he thought he wanted a nice relationship, but he mostly wanted to get his end away. Being 19, that's kind of fair enough. But still.
Bottom line is that it doesn't seem to have much to do with age, but it does have to do with experience. A lot of people today will feel trapped and stifled if their first relationship gets very serious, and they haven't played the field, because they'll wonder what they're missing. Certainly wouldn't have said it's to do with "running out of options" though...