Obviously a guy isn't going to date a girl much older than him. But I'd say a 2-3 year difference between girl and guy (girl being the younger one) is ok for people aged 20+.
The topic title is misleading ^^^ not really "intelligence" as in IQ but as in what you're studying.
ok so this sort of question doesn't really come up often but...
Let's just say there's a girl doing Medicine at (let's be stereotypical) UNSW. And there's a boy in UNSW but he does Commerce...