Arre chess, look man, you're 20-something, right? Remember how it was when we were in high school/college? You liked a girl, she liked you, and you ran around the whole day wondering when you'd get to see her again, etc etc. And then those pre-planned meetings in quiet places, just the two of you walking around aimlessly, and tension so thick you could cut it with a lightsabre and watch it glue back like Fevi? DID YOU EVER TELL YOUR PARENTS THEN??? Nien, I'm guessing, so why do you have to tell 'em now? Just talk with the chick, gauge whether she fancies you, and then spend time together as often as you can. If you're planning on trying to hold on to her for the next five years and then get engaged, dude, I'm afraid you're gonna be closing your mind. Who knows, in the next five years, you'll find someone else you'll fall for so hard we'll have to dig you out of the mantle. And what if she finds someone else? What if you realise sis 'n you aren't compatible? What if I pass in fluid mechanics? If you tell your rents now, either they'll flip (hopefully not, but i had to put it in there), or they'll think about it and say, "Yeah, okay", and keep a close -correction, very close- eye on you for the rest of your days. And if in FIVE YEARS (say that again, loudly), another chick comes along? Your whole family'll think you dumped second-cuz for that one, and you'll have a rep - albeit a bad one. Like one of those criminal records. Great, now I've lost my thread. Okay, all i'm saying is that, take it easy, do not, I repeat, DO NOT tell mum 'n dad right now, and see how things go. Keep us updated
Just my two cents worth...