It has one of the best character arcs in cinema, and in many respects is timeless.
And he clings to this woman in an affair that makes him feel like he's doing something 'adult,' and he thinks that she gets it. And he soon realizes that she's clinging to him for youth.
If you follow the character arc, it's not jumpy or nonsensical. It's a kid who think he's at the point in his life where things are supposed to make sense; when the adult switch is supposed to flip on. He tries to force his way into adulthood, only to realize that there's no such thing. He jumps into an affair because Mrs. Robinson seems so together, only to realize that she's with him because she's not at all together. The adults don't 'get it' either, and are rushing in the other direction to retain their youth. And man, that last shot, where the both realize how hopelessly they don't get it. That by trying to force your way to somewhere that you're just not feeling, you surely wind up in the wrong spot.
From that opening shot, where everyone and everything at the party is completely alien, old, and comfortable to him, yet they're all acting like it should be familiar now that he's a graduate. The whole movie exposes how messy life really is and gets to the heart of the difficulty of transitions.
I'd recommend not looking at Ben as a hero at all. He's just a guy who's being told he's an adult, but doesn't feel that way. He feels like everybody gets it but him. And by the end, he realizes that nobody gets it. Or at least, if they get one thing, they don't get lots of other things.
It's a perfect reflection of how messy life in contemporary America is.