I rode centuries on my half-bike before I became a stoker. Captain had never done more than a metric on any bike when we did the Palm Springs century in '07. He felt so good after that that we did a century a month from Feb.-October.
I think it depends on the individual -- if they want to ride a solo century, they will. But just because you can ride a century solo, doesn't mean you should, unless you really want to -- otherwise it's a long, lonely ride.