To throw some support in Beni's direction, I think his overall point can be taken without demanding some kind of technical correctness. Since when has Star Wars cared about anything making sense scientifically? SW has always been more about spiritual mumbo jumbo than science, and Lucas' major attempt at science fiction - the midichlorians - is pretty ridiculous. And moreover, as Freshest said, we don't understand aging very well, and in the Star Wars universe, biology has this whole other midichlorians thing going on which means we really, really don't know what the F is going on.
I can dig what I see to be the main idea, which is that at 30 people generally have more vitality than at 80. And since the Force is all about life, vitality might be connected to one's ability to channel it. Details schmetails!